Heterocyclic Compound, Light-Emitting Element, Light-Emitting Device, Electronic Device, and Lighting Device

ABSTRACT

A novel heterocyclic compound that can be used as a host material in which a light-emitting substance is dispersed. A light-emitting element having a long lifetime. A heterocyclic compound in which a substituted or unsubstituted dibenzo[f,h]quinoxalinyl group is bonded to a substituted or unsubstituted arylene group having 6 to 25 carbon atoms which is bonded to any one of the 8-11 positions of a substituted or unsubstituted benzo[b]naphtho[1,2-d]furan skeleton.

This application is a continuation of copending U.S. application Ser.No. 14/468,954, filed on Aug. 26, 2014, which is incorporated herein byreference.

TECHNICAL FIELD

The present invention relates to an object, a method, or a manufacturingmethod. In addition, the present invention relates to a process, amachine, manufacture, or a composition of matter. One embodiment of thepresent invention relates to a semiconductor device, a display device, alight-emitting device, a lighting device, a driving method thereof, or amanufacturing method thereof. In particular, one embodiment of thepresent invention relates to a heterocyclic compound, a light-emittingelement utilizing electroluminescence (EL) (the light-emitting elementis also referred to as an EL element), a light-emitting device, anelectronic device, and a lighting device.

BACKGROUND ART

In recent years, a light-emitting element using an organic compound as alight-emitting substance (the light-emitting element is also referred toas an organic EL element) has been actively researched and developed. Ina basic structure of the light-emitting element, a layer containing alight-emitting substance is provided between a pair of electrodes.Voltage application to this element causes the light-emitting substanceto emit light.

The light-emitting element is a self-luminous element and thus hasadvantages over a liquid crystal display element, such as highvisibility of the pixels and no need of backlight, and is considered tobe suitable as a flat panel display element. Another major advantage ofthe light-emitting element is that it can be fabricated to be thin andlightweight. Besides, the light-emitting element has an advantage ofquite high response speed.

Since the light-emitting element can be formed in a film form, planarlight emission can be provided; thus, a large-area element can be easilyformed. This feature is difficult to obtain with point light sourcestypified by incandescent lamps and LEDs or linear light sources typifiedby fluorescent lamps. Thus, the light-emitting element also has greatpotential as a planar light source applicable to a lighting device andthe like.

In the case of a light-emitting element in which a layer containing anorganic compound used as a light-emitting substance is provided betweena pair of electrodes, by applying a voltage to the element, electronsfrom a cathode and holes from an anode are injected into the layercontaining the organic compound and thus a current flows. The injectedelectrons and holes then lead the organic compound to its excited state,so that light emission is provided from the excited organic compound.

The excited state formed by an organic compound can be a singlet excitedstate or a triplet excited state. Light emission from the singletexcited state (S*) is called fluorescence, and light emission from thetriplet excited state (T*) is called phosphorescence. The statisticalgeneration ratio thereof in the light-emitting element is considered tobe S*:T*=1:3.

At room temperature, a compound capable of converting a singlet excitedstate into light emission (hereinafter, referred to as a fluorescentcompound) exhibits only light emission from the singlet excited state(fluorescence), and light emission from the triplet excited state(phosphorescence) cannot be observed. Accordingly, the internal quantumefficiency (the ratio of the number of generated photons to the numberof injected carriers) of a light-emitting element including thefluorescent compound is assumed to have a theoretical limit of 25%, onthe basis of S*:T*=1:3.

In contrast, a compound capable of converting a triplet excited stateinto light emission (hereinafter, referred to as a phosphorescentcompound) exhibits light emission from the triplet excited state(phosphorescence). Furthermore, since intersystem crossing (i.e.,transition from a singlet excited state to a triplet excited state)easily occurs in a phosphorescent compound, the internal quantumefficiency can be theoretically increased to 100%. That is, higheremission efficiency can be achieved than using a fluorescent compound.For this reason, light-emitting elements using a phosphorescent compoundhave been under active development recently so that high-efficiencylight-emitting elements can be achieved.

When a light-emitting layer of a light-emitting element is formed usingthe phosphorescent compound described above, in order to inhibitconcentration quenching or quenching due to triplet-triplet annihilationof the phosphorescent compound, the light-emitting layer is usuallyformed such that the phosphorescent compound is dispersed in a matrix ofanother compound. Here, the compound serving as the matrix is calledhost material, and the compound dispersed in the matrix like thephosphorescent compound is called guest material.

When a phosphorescent compound is a guest material, a host materialneeds to have higher triplet excitation energy (energy differencebetween a ground state and a triplet excited state) than thephosphorescent compound.

Furthermore, since singlet excitation energy (energy difference betweena ground state and a singlet excited state) is higher than tripletexcitation energy, a substance that has high triplet excitation energyalso has high singlet excitation energy. Thus, the above substance thathas high triplet excitation energy is also effective in a light-emittingelement using a fluorescent compound as a light-emitting substance.

Studies have been conducted on compounds having dibenzo[f,h]quinoxalinerings, which are examples of the host material used when aphosphorescent compound is a guest material (e.g., see Patent Documents1 and 2).

REFERENCE Patent Document

[Patent Document 1] International Publication WO 03/058667 pamphlet

[Patent Document 2] Japanese Published Patent Application No.2007-189001

DISCLOSURE OF INVENTION

In improving element characteristics of a light-emitting element, thereare many problems which depend on substances used for the light-emittingelement. Therefore, improvement in an element structure, development ofa substance, and the like have been carried out in order to solve theproblems. Development of light-emitting elements leaves room forimprovement in terms of emission efficiency, reliability, cost, and thelike.

For practical use of a display or lighting which uses a light-emittingelement, a long lifetime of the light-emitting element has beenrequired.

In view of the above, an object of one embodiment of the presentinvention is to provide a novel heterocyclic compound. An object of oneembodiment of the present invention is to provide a novel heterocycliccompound which can be used in a light-emitting element as a hostmaterial in which a light-emitting substance is dispersed. An object ofone embodiment of the present invention is to provide a heterocycliccompound having high triplet excitation energy.

An object of one embodiment of the present invention is to provide alight-emitting element with high emission efficiency. An object of oneembodiment of the present invention is to provide a light-emittingelement with low drive voltage. An object of one embodiment of thepresent invention is to provide a light-emitting element having a longlifetime. An object of one embodiment of the present invention is toprovide a novel light-emitting element.

An object of one embodiment of the present invention is to provide ahighly reliable light-emitting device, a highly reliable electronicdevice, or a highly reliable lighting device using the light-emittingelement. An object of one embodiment of the present invention is toprovide a light-emitting device, an electronic device, or a lightingdevice with low power consumption using the light-emitting element.

In one embodiment of the present invention, there is no need to achieveall the objects.

One embodiment of the present invention is a heterocyclic compoundrepresented by General Formula (G1).

In the formula, one of R⁷ to R¹⁰ represents a substituent represented byGeneral Formula (G1-1); R¹ to R⁶ and the others of R⁷ to R¹⁰ separatelyrepresent any one of hydrogen, an alkyl group having 1 to 6 carbonatoms, a cycloalkyl group having 3 to 6 carbon atoms, and an aryl grouphaving 6 to 13 carbon atoms; A represents a dibenzo[f,h]quinoxalinylgroup; and Ar represents an arylene group having 6 to 25 carbon atoms.The dibenzo[f,h]quinoxalinyl group, the aryl group, and the arylenegroup are separately unsubstituted or substituted by any one of an alkylgroup having 1 to 6 carbon atoms, a cycloalkyl group having 3 to 6carbon atoms, and an aryl group having 6 to 13 carbon atoms.

One embodiment of the present invention is a heterocyclic compoundrepresented by General Formula (G2).

In the formula, R¹ to R⁹ separately represent any one of hydrogen, analkyl group having 1 to 6 carbon atoms, a cycloalkyl group having 3 to 6carbon atoms, and an aryl group having 6 to 13 carbon atoms; Arepresents a dibenzo[f,h]quinoxalinyl group; and Ar represents anarylene group having 6 to 25 carbon atoms. The dibenzo[f,h]quinoxalinylgroup, the aryl group, and the arylene group are separatelyunsubstituted or substituted by any one of an alkyl group having 1 to 6carbon atoms, a cycloalkyl group having 3 to 6 carbon atoms, and an arylgroup having 6 to 13 carbon atoms.

One embodiment of the present invention is a heterocyclic compoundrepresented by General Formula (G3).

In the formula, R¹ to R⁹ and R¹¹ to R¹⁹ separately represent any one ofhydrogen, an alkyl group having 1 to 6 carbon atoms, a cycloalkyl grouphaving 3 to 6 carbon atoms, and an aryl group having 6 to 13 carbonatoms, and Ar represents an arylene group having 6 to 25 carbon atoms.The aryl group and the arylene group are separately unsubstituted orsubstituted by any one of an alkyl group having 1 to 6 carbon atoms, acycloalkyl group having 3 to 6 carbon atoms, and an aryl group having 6to 13 carbon atoms.

One embodiment of the present invention is a light-emitting elementincluding a layer that contains any of the heterocyclic compounds havingthe above structures.

One embodiment of the present invention is a light-emitting deviceincluding the above-described light-emitting element in a light-emittingportion. One embodiment of the present invention is an electronic deviceincluding the light-emitting device in a display portion. One embodimentof the present invention is a lighting device including thelight-emitting device in a light-emitting portion.

The light-emitting device in this specification includes an imagedisplay device that uses a light-emitting element. The category of thelight-emitting device in this specification includes a module in which alight-emitting element is provided with a connector such as ananisotropic conductive film or a tape carrier package (TCP); a module inwhich a printed wiring board is provided at the end of a TCP; and amodule in which an integrated circuit (IC) is directly mounted on alight-emitting element by a chip on glass (COG) method. In addition, alight-emitting device that is used in lighting equipment and the likeare also included.

An organic compound represented by General Formula (G4), which is usedin synthesis of the heterocyclic compound of one embodiment of thepresent invention, is also one embodiment of the present invention.

In the formula, one of R⁷ to R¹⁰ represents a substituent represented byGeneral Formula (G4-1); R¹ to R⁶ and the others of R⁷ to R₁₀ separatelyrepresent any one of hydrogen, an alkyl group having 1 to 6 carbonatoms, a cycloalkyl group having 3 to 6 carbon atoms, and an aryl grouphaving 6 to 13 carbon atoms; and R²⁰ and R²¹ separately represent anyone of a hydroxyl group and an alkoxy group having 1 to 6 carbon atomsand may be bonded to each other to form a ring. The aryl group and thealkoxy group are separately unsubstituted or substituted by any one ofan alkyl group having 1 to 6 carbon atoms, a cycloalkyl group having 3to 6 carbon atoms, and an aryl group having 6 to 13 carbon atoms.

An organic compound represented by Structural Formula (201), which isused in synthesis of the heterocyclic compound of one embodiment of thepresent invention, is also one embodiment of the present invention.

In one embodiment of the present invention, a heterocyclic compoundhaving high triplet excitation energy can be provided. In one embodimentof the present invention, a novel heterocyclic compound which can beused in a light-emitting element as a host material in which alight-emitting substance is dispersed can be provided. In one embodimentof the present invention, a light-emitting element that has a longlifetime can be provided.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A to 1D each illustrate an example of a light-emitting element ofone embodiment of the present invention.

FIGS. 2A and 2B illustrate an example of a light-emitting device of oneembodiment of the present invention.

FIGS. 3A to 3C illustrate examples of a light-emitting device of oneembodiment of the present invention.

FIGS. 4A to 4E illustrate examples of an electronic device.

FIGS. 5A and 5B illustrate examples of a lighting device.

FIGS. 6A and 6B show ¹H NMR charts of2-(benzo[b]naphtho[1,2-d]furan-8-yl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane.

FIGS. 7A and 7B show ¹H NMR charts of2-{3-[3-(benzo[b]naphtho[1,2-d]furan-8-yl)phenyl]phenyl}dibenzo[f,h]quinoxaline(abbreviation: 2mBnfBPDBq).

FIGS. 8A and 8B show an absorption spectrum and an emission spectrum ofa toluene solution of 2mBnfBPDBq.

FIGS. 9A and 9B show an absorption spectrum and an emission spectrum ofa thin film of 2mBnfBPDBq.

FIGS. 10A and 10B show CV measurement results of 2mBnfBPDBq.

FIGS. 11A and 11B show results of LC-MS analysis of 2mBnfBPDBq.

FIG. 12 illustrates a light-emitting element of Examples.

FIG. 13 is a graph showing luminance-current density characteristics ofa light-emitting element in Example 3.

FIG. 14 is a graph showing luminance-voltage characteristics of alight-emitting element in Example 3.

FIG. 15 is a graph showing current efficiency-luminance characteristicsof a light-emitting element in Example 3.

FIG. 16 is a graph showing current-voltage characteristics of alight-emitting element in Example 3.

FIG. 17 is a graph showing external quantum efficiency-luminancecharacteristics of a light-emitting element in Example 3.

FIG. 18 shows results of a reliability test of a light-emitting elementin Example 3.

FIG. 19 is a graph showing luminance-current density characteristics ofa light-emitting element in Example 4.

FIG. 20 is a graph showing luminance-voltage characteristics of alight-emitting element in Example 4.

FIG. 21 is a graph showing current efficiency-luminance characteristicsof a light-emitting element in Example 4.

FIG. 22 is a graph showing current-voltage characteristics of alight-emitting element in Example 4.

FIG. 23 is a graph showing external quantum efficiency-luminancecharacteristics of a light-emitting element in Example 4.

FIG. 24 shows results of a reliability test of a light-emitting elementin Example 4.

FIGS. 25A and 25B show ¹H NMR charts of2-[3′-(6-phenylbenzo[b]naphtho[1,2-d]furan-8-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline(abbreviation: 2mBnfBPDBq-02).

FIGS. 26A and 26B show an absorption spectrum and an emission spectrumof a toluene solution of 2mBnfBPDBq-02.

FIGS. 27A and 27B show an absorption spectrum and an emission spectrumof a thin film of 2mBnfBPDBq-02.

FIGS. 28A and 28B show CV measurement results of 2mBnfBPDBq-02.

FIG. 29 is a graph showing luminance-current density characteristics ofa light-emitting element in Example 6.

FIG. 30 is a graph showing luminance-voltage characteristics of alight-emitting element in Example 6.

FIG. 31 is a graph showing current efficiency-luminance characteristicsof a light-emitting element in Example 6.

FIG. 32 is a graph showing current-voltage characteristics of alight-emitting element in Example 6.

FIG. 33 is a graph showing external quantum efficiency-luminancecharacteristics of a light-emitting element in Example 6.

FIG. 34 shows results of a reliability test of a light-emitting elementin Example 6.

FIGS. 35A and 35B show results of LC-MS analysis of 2mBnfBPDBq-02.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described with reference tothe drawings. Note that the present invention is not limited to thefollowing description, and it is easily understood by those skilled inthe art that various changes for embodiments and details can be madewithout departing from the spirit and scope of the invention. Therefore,the present invention should not be construed as being limited to thedescription in the following embodiments.

Note that in the structures of the invention described below, the sameportions or portions having similar functions are denoted by the samereference numerals in different drawings, and description of suchportions is not repeated. Furthermore, the same hatching pattern isapplied to portions having similar functions, and the portions are notespecially denoted by reference numerals in some cases.

In addition, the position, size, range, or the like of each structureillustrated in drawings and the like is not accurately represented insome cases for easy understanding. Therefore, the disclosed invention isnot necessarily limited to the position, the size, the range, or thelike disclosed in the drawings and the like.

Embodiment 1

In this embodiment, a heterocyclic compound of one embodiment of thepresent invention is described.

One embodiment of the present invention is a heterocyclic compound inwhich a dibenzo[f,h]quinoxaline skeleton and abenzo[b]naphtho[1,2-d]furan skeleton are bonded through an aryleneskeleton.

A dibenzo[f,h]quinoxaline skeleton has a planar structure. An organiccompound having a planar structure is easily crystallized. Alight-emitting element using an organic compound that is easilycrystallized has a short lifetime. However, the heterocyclic compound ofone embodiment of the present invention has a sterically bulky structuresince a benzo[b]naphtho[1,2-d]furan skeleton is bonded to adibenzo[f,h]quinoxaline skeleton through an arylene skeleton. Theheterocyclic compound of one embodiment of the present invention is noteasily crystallized, which can inhibit a reduction in lifetime of alight-emitting element. By including a benzo[b]naphtho[1,2-d]furanskeleton, in which a benzene ring and a naphthalene ring are condensedwith a furan skeleton, and a dibenzo[f,h]quinoxaline skeleton, in whichtwo benzene rings are condensed with a quinoxaline skeleton, theheterocyclic compound of one embodiment of the present invention hasextremely high heat resistance, and when the heterocyclic compound isused in a light-emitting element, the light-emitting element can havehigh heat resistance and a long lifetime.

When a compound that cannot easily accept electrons or holes is used asa host material in a light-emitting layer, the regions of electron-holerecombination concentrate on an interface between the light-emittinglayer and a different layer, leading to a reduction in lifetime of alight-emitting element. Here, the heterocyclic compound of oneembodiment of the present invention can easily accept electrons andholes since the heterocyclic compound has a dibenzo[f,h]quinoxalineskeleton as an electron-transport skeleton and abenzo[b]naphtho[1,2-d]furan skeleton as a hole-transport skeleton.Accordingly, by the use of the heterocyclic compound of one embodimentof the present invention as the host material of the light-emittinglayer, electrons and holes presumably recombine in a wide region of thelight-emitting layer and it is possible to inhibit a reduction inlifetime of the light-emitting element.

As compared to extension of a conjugated system in a heterocycliccompound in which a dibenzo[f,h]quinoxaline skeleton and abenzo[b]naphtho[1,2-d]furan skeleton are directly bonded, extension of aconjugated system in the heterocyclic compound of one embodiment of thepresent invention in which the two skeletons are bonded through anarylene group is small; accordingly, reductions in band gap and tripletexcitation energy can be prevented. Moreover, the heterocyclic compoundof one embodiment of the present invention is also advantageous in thatits heat resistance and film quality are high.

The heterocyclic compound of one embodiment of the present invention hasa wide band gap. Accordingly, the heterocyclic compound can be favorablyused as a host material, in which a light-emitting substance isdispersed, of a light-emitting layer in a light-emitting element.Furthermore, since the heterocyclic compound of one embodiment of thepresent invention has triplet excitation energy high enough to excite aphosphorescent compound emitting light in a wavelength range from red togreen, the heterocyclic compound can be favorably used as a hostmaterial in which the phosphorescent compound is dispersed.

Furthermore, since the heterocyclic compound of one embodiment of thepresent invention has a high electron-transport property, theheterocyclic compound can be suitably used as a material for anelectron-transport layer in a light-emitting element.

Thus, the heterocyclic compound of one embodiment of the presentinvention can be suitably used as a material for an organic device suchas a light-emitting element or an organic transistor.

One embodiment of the present invention is a heterocyclic compoundrepresented by General Formula (G1). In the case where a substituentrepresented by General Formula (G1-1) is bonded to the benzene ring ofbenzo[b]naphtho[1,2-d]furan, the heterocyclic compound can have a highertriplet excitation energy level (T₁ level) than in the case where thesubstituent is bonded to the naphthalene ring (than in the case where R¹is the substituent, particularly).

In the formula, R¹ to R⁶ separately represent any one of hydrogen, analkyl group having 1 to 6 carbon atoms, a cycloalkyl group having 3 to 6carbon atoms, and an aryl group having 6 to 13 carbon atoms; one of R⁷to R¹⁰ represents a substituent represented by General Formula (G1-1);the others of R⁷ to R¹⁰ separately represent any one of hydrogen, analkyl group having 1 to 6 carbon atoms, a cycloalkyl group having 3 to 6carbon atoms, and an aryl group having 6 to 13 carbon atoms; Arepresents a dibenzo[f,h]quinoxalinyl group; and Ar represents anarylene group having 6 to 25 carbon atoms. The dibenzo[f,h]quinoxalinylgroup, the aryl group, and the arylene group are separatelyunsubstituted or substituted by any one of an alkyl group having 1 to 6carbon atoms, a cycloalkyl group having 3 to 6 carbon atoms, and an arylgroup having 6 to 13 carbon atoms.

In particular, the substituent represented by General Formula (G1-1) ispreferably bonded to the 8-position of benzo[b]naphtho[1,2-d]furanskeleton in General Formula (G1) (that is, R¹⁰ in General Formula (G1)is preferably the substituent represented by General Formula (G1-1))because a high T₁ level can be achieved.

Specifically, one embodiment of the present invention is a heterocycliccompound represented by General Formula (G2).

In the formula, R¹ to R⁹ separately represent any one of hydrogen, analkyl group having 1 to 6 carbon atoms, a cycloalkyl group having 3 to 6carbon atoms, and an aryl group having 6 to 13 carbon atoms; Arepresents a dibenzo[f,h]quinoxalinyl group; and Ar represents anarylene group having 6 to 25 carbon atoms. The dibenzo[f,h]quinoxalinylgroup, the aryl group, and the arylene group are separatelyunsubstituted or substituted by any one of an alkyl group having 1 to 6carbon atoms, a cycloalkyl group having 3 to 6 carbon atoms, and an arylgroup having 6 to 13 carbon atoms.

In the heterocyclic compound represented by General Formula (G2), Ar ispreferably bonded to the 2-position, the 6-position, or the 7-positionof the dibenzo[f,h]quinoxaline skeleton for easier synthesis, higherpurity, a higher T₁ level, and the like. Ar is preferably bonded to the2-position because the heterocyclic compound can be more easilysynthesized and can have high purity more easily and thus can beprovided at lower cost than in the case where Ar is bonded to the6-position or the 7-position. Ar is preferably bonded to the 6-positionbecause a T₁ level can be higher than in the case where Ar is bonded tothe 2-position or the 7-position. Ar is preferably bonded to the7-position because a T₁ level can be higher than in the case where Ar isbonded to the 2-position.

One embodiment of the present invention is a heterocyclic compoundrepresented by General Formula (G3).

In the formula, R¹ to R⁹ and R¹¹ to R¹⁹ separately represent any one ofhydrogen, an alkyl group having 1 to 6 carbon atoms, a cycloalkyl grouphaving 3 to 6 carbon atoms, and an aryl group having 6 to 13 carbonatoms, and Ar represents an arylene group having 6 to 25 carbon atoms.The aryl group and the arylene group are separately unsubstituted orsubstituted by any one of an alkyl group having 1 to 6 carbon atoms, acycloalkyl group having 3 to 6 carbon atoms, and an aryl group having 6to 13 carbon atoms. At least one of R¹ to R⁹ is preferably a benzenering because higher heat resistance can be achieved. Specifically, R¹ ispreferably a phenyl group because the synthesis is facilitated. Examplesof a heterocyclic compound with such a structure include the compounddescribed later in Synthesis Example 2.

Specific examples of the structure of Ar in General Formulae (G1-1),(G2), and (G3) include substituents represented by Structural Formulae(1-1) to (1-18). Note that Ar may further have, as a substituent, anyone of an alkyl group having 1 to 4 carbon atoms, a cycloalkyl grouphaving 3 to 6 carbon atoms, and an aryl group having 6 to 13 carbonatoms. As examples of the aryl group having 6 to 13 carbon atoms, aphenyl group, a naphthyl group, a fluorenyl group, and the like can begiven. Specific examples of Ar having a substituent are illustrated byStructural Formulae (1-12), (1-13), (1-15), and (1-18). Note that Arhaving a substituent is not limited to these examples.

Ar preferably has one or more kinds of rings selected from a benzenering, a fluorene ring, and a naphthalene ring. Ar is preferably asubstituent including one or more kinds of rings selected from a benzenering, a fluorene ring, and a naphthalene ring, examples of which includea phenylene group, a biphenylene group, a terphenylene group, aquaterphenylene group, a naphthalene-diyl group, and a 9H-fluoren-diylgroup. In that case, the heterocyclic compound of one embodiment of thepresent invention can have high triplet excitation energy.

Specific examples of R¹ to R¹⁹ in General Formulae (G1) to (G3) includesubstituents represented by Structural Formulae (2-1) to (2-23). Notethat when R¹ to R¹⁹ represent aryl groups, R¹ to R¹⁹ may further have,as a substituent, any one of an alkyl group having 1 to 4 carbon atoms,a cycloalkyl group having 3 to 6 carbon atoms, and an aryl group having6 to 13 carbon atoms. As examples of the aryl group having 6 to 13carbon atoms, a phenyl group, a naphthyl group, a fluorenyl group, andthe like can be given. Specific examples of the aryl group having asubstituent are illustrated by Structural Formulae (2-13) to (2-22).Note that R¹ to R¹⁹ each having a substituent are not limited to theseexamples.

Specific examples of the heterocyclic compound of one embodiment of thepresent invention include heterocyclic compounds represented byStructural Formulae (100) to (155). However, the present invention isnot limited to these structural formulae.

A variety of reactions can be applied to a method for synthesizing theheterocyclic compound of one embodiment of the present invention. As anexample, a method for synthesizing the heterocyclic compound representedby General Formula (G1) in which R¹⁰ is the substituent represented byGeneral formula (G1-1), i.e., a method for synthesizing the heterocycliccompound represented by General Formula (G2), is described below. Notethat the methods for synthesizing the heterocyclic compound of oneembodiment of the present invention are not limited to the synthesismethods below.

The heterocyclic compound represented by General Formula (G2) can besynthesized under Synthesis Scheme (A-1) below. That is, theheterocyclic compound represented by General Formula (G2) can beobtained by coupling of a benzo[b]naphtho[1,2-d]furan compound(Compound 1) and a dibenzo[f,h]quinoxaline compound (Compound 2).

In Synthesis Scheme (A-1), A represents a substituted or unsubstituteddibenzo[f,h]quinoxalinyl group; Ar represents a substituted orunsubstituted arylene group having 6 to 25 carbon atoms; X¹ and X²separately represent any one of a halogen, a trifluoromethanesulfonylgroup, a boronic acid group, an organoboron group, a halogenatedmagnesium group, an organotin group, and the like; and R¹ to R⁹separately represent any one of hydrogen, an alkyl group having 1 to 6carbon atoms, and a substituted or unsubstituted aryl group having 6 to13 carbon atoms.

When a Suzuki-Miyaura coupling reaction using a palladium catalyst isperformed under Synthesis Scheme (A-1), X¹ and X² separately representany one of a halogen, a boronic acid group, an organoboron group, and atrifluoromethanesulfonyl group. It is preferable that the halogen be anyone of iodine, bromine, and chlorine. In the reaction, a palladiumcompound such as bis(dibenzylideneacetone)palladium(0) or palladium(II)acetate and a ligand such as tri(tert-butyl)phosphine,tri(n-hexyl)phosphine, tricyclohexylphosphine,di(1-adamantyl)-n-butylphosphine,2-dicyclohexylphosphino-2′,6′-dimethoxybiphenyl, ortri(ortho-tolyl)phosphine can be used. In addition, in the reaction, anorganic base such as sodium tert-butoxide, an inorganic base such aspotassium carbonate, cesium carbonate, or sodium carbonate, or the likecan be used. Furthermore, in the reaction, toluene, xylene, benzene,tetrahydrofuran, dioxane, ethanol, methanol, water, or the like can beused as a solvent. Reagents that can be used in the reaction are notlimited thereto.

The reaction performed under Synthesis Scheme (A-1) is not limited to aSuzuki-Miyaura coupling reaction, and a Migita-Kosugi-Stille couplingreaction using an organotin compound, a Kumada-Tamao-Corriu couplingreaction using a Grignard reagent, a Negishi coupling reaction using anorganozinc compound, a reaction using copper or a copper compound, orthe like can also be employed.

By a method similar to the above, it is also possible to synthesize aheterocyclic compound in which the substituent represented by GeneralFormula (G1-1) is bonded to the 9-position, the 10-position, or the11-position of benzo[b]naphtho[1,2-d]furan (i.e., a heterocycliccompound represented by General Formula (G1) in which R⁷, R⁸, or R⁹represents the substituent represented by General Formula (G1-1)).

Specifically, when R⁷, R⁸, or R⁹ of Compound 1 in Synthesis Scheme (A-1)represents any one of a halogen, a trifluoromethanesulfonyl group, aboronic acid group, an organoboron group, a halogenated magnesium group,an organotin group, and the like, by causing a coupling reaction similarto that performed under Synthesis Scheme (A-1), it is possible tosynthesize a heterocyclic compound in which the substituent representedby General Formula (G1-1) and including a dibenzo[f,h]quinoxalineskeleton is bonded to the 9-position, the 10-position, or the11-position of benzo[b]naphtho[1,2-d]furan, i.e., the heterocycliccompound represented by General Formula (G1) in which R⁷, R⁸, or R⁹represents the substituent represented by General Formula (G1-1).

In synthesis of the heterocyclic compound represented by General Formula(G2), Ar may be coupled at the 8-position of thebenzo[b]naphtho[1,2-d]furan skeleton, and then, the resulting compoundmay be coupled with a dibenzo[f,h]quinoxaline skeleton.

Thus, the heterocyclic compound of this embodiment can be synthesized.

An organoboron compound in which boron is bonded to any one of the 7- to10-positions of benzo[b]naphtho[1,2-d]furan and which is used insynthesis of the heterocyclic compound of one embodiment of the presentinvention is also one embodiment of the present invention.

One embodiment of the present invention is an organoboron compoundrepresented by General Formula (G4).

In the formula, R¹ to R⁶ separately represent any one of hydrogen, analkyl group having 1 to 6 carbon atoms, a cycloalkyl group having 3 to 6carbon atoms, and an aryl group having 6 to 13 carbon atoms; one of R⁷to R¹⁰ represents a substituent represented by General Formula (G4-1);the others of R⁷ to R¹⁰ separately represent any one of hydrogen, analkyl group having 1 to 6 carbon atoms, a cycloalkyl group having 3 to 6carbon atoms, and an aryl group having 6 to 13 carbon atoms; and R²⁰ andR²¹ separately represent any one of a hydroxyl group and an alkoxy grouphaving 1 to 6 carbon atoms and may be bonded to each other to form aring. The aryl group and the alkoxy group are separately unsubstitutedor substituted by any one of an alkyl group having 1 to 6 carbon atoms,a cycloalkyl group having 3 to 6 carbon atoms, and an aryl group having6 to 13 carbon atoms.

Specific examples of the organoboron compound of one embodiment of thepresent invention include organoboron compounds represented byStructural Formulae (200) to (207). However, the present invention isnot limited to these structural formulae. Structural Formulae (201),(203), (205), and (207) illustrate specific examples of the case whereR²⁰ and R²¹ in General Formula (G4-1) each represent a substitutedalkoxy group having 1 to 6 carbon atoms and the case where R²⁰ and R²¹are bonded to each other to form a ring.

In a light-emitting element, the heterocyclic compound of thisembodiment can be favorably used as a host material of a light-emittinglayer, in which a light-emitting substance is dispersed, or a materialof an electron-transport layer. By the use of the heterocyclic compoundof this embodiment, a light-emitting element with a long lifetime can beprovided.

This embodiment can be combined with any other embodiment asappropriate.

Embodiment 2

In this embodiment, light-emitting elements of embodiments of thepresent invention will be described with reference to FIGS. 1A to 1D.

A light-emitting element of one embodiment of the present invention hasa layer containing the heterocyclic compound described in Embodiment 1between a pair of electrodes.

The heterocyclic compound included in the light-emitting element of oneembodiment of the present invention is sterically bulky and highlyresistant to heat. Accordingly, the use of the heterocyclic compoundenables a light-emitting element to have a long lifetime.

Furthermore, the heterocyclic compound can accept electrons and holessince the heterocyclic compound has a dibenzo[f,h]quinoxaline skeletonas an electron-transport skeleton and a benzo[b]naphtho[1,2-d]furanskeleton as a hole-transport skeleton. Accordingly, by the use of theheterocyclic compound as a host material of a light-emitting layer,electrons and holes recombine in the light-emitting layer and it ispossible to inhibit a reduction in lifetime of the light-emittingelement. That is, a preferred embodiment of the present invention is alight-emitting element including, between a pair of electrodes, alight-emitting layer containing a light-emitting substance (guestmaterial) and the above heterocyclic compound serving as a host materialin which the light-emitting substance is dispersed.

The light-emitting element of this embodiment includes a layer (ELlayer) containing a light-emitting organic compound between a pair ofelectrodes (a first electrode and a second electrode). One of the firstelectrode and the second electrode functions as an anode, and the otherfunctions as a cathode. In this embodiment, the EL layer contains theheterocyclic compound of one embodiment of the present invention whichis described in Embodiment 1.

<<Structural Example of Light-Emitting Element>>

A light-emitting element illustrated in FIG. 1A includes an EL layer 203between a first electrode 201 and a second electrode 205. In thisembodiment, the first electrode 201 serves as an anode and the secondelectrode 205 serves as a cathode.

When a voltage higher than the threshold voltage of the light-emittingelement is applied between the first electrode 201 and the secondelectrode 205, holes are injected from the first electrode 201 side tothe EL layer 203 and electrons are injected from the second electrode205 side to the EL layer 203. The injected electrons and holes recombinein the EL layer 203 and a light-emitting substance contained in the ELlayer 203 emits light.

The EL layer 203 includes at least a light-emitting layer 303 containinga light-emitting substance.

Furthermore, when a plurality of light-emitting layers are provided inthe EL layer and emission colors of the layers are made different, lightemission of a desired color can be provided from the light-emittingelement as a whole. For example, the emission colors of first and secondlight-emitting layers are complementary in a light-emitting elementhaving the two light-emitting layers, so that the light-emitting elementcan be made to emit white light as a whole. Note that “complementarycolors” refer to colors that can produce an achromatic color when mixed.In other words, when light components obtained from substances that emitlight of complementary colors are mixed, white emission can be obtained.Furthermore, the same applies to a light-emitting element having threeor more light-emitting layers.

In addition to the light-emitting layer, the EL layer 203 may furtherinclude a layer containing a substance with a high hole-injectionproperty, a substance with a high hole-transport property, a substancewith a high electron-transport property, a substance with a highelectron-injection property, a substance with a bipolar property (asubstance with a high electron-transport property and a highhole-transport property), or the like. Either a low molecular compoundor a high molecular compound can be used for the EL layer 203, and aninorganic compound may be used.

A light-emitting element illustrated in FIG. 1B includes the EL layer203 between the first electrode 201 and the second electrode 205, and inthe EL layer 203, a hole-injection layer 301, a hole-transport layer302, the light-emitting layer 303, an electron-transport layer 304, andan electron-injection layer 305 are stacked in that order from the firstelectrode 201 side.

The heterocyclic compound of one embodiment of the present invention ispreferably used for the light-emitting layer 303 or theelectron-transport layer 304. In this embodiment, an example isdescribed in which the heterocyclic compound of one embodiment of thepresent invention is used as the host material in the light-emittinglayer 303.

As in light-emitting elements illustrated in FIGS. 1C and 1D, aplurality of EL layers may be stacked between the first electrode 201and the second electrode 205. In this case, an intermediate layer 207 ispreferably provided between the stacked EL layers. The intermediatelayer 207 includes at least a charge-generation region.

For example, the light-emitting element illustrated in FIG. 1C includesthe intermediate layer 207 between a first EL layer 203 a and a secondEL layer 203 b. The light-emitting element illustrated in FIG. 1Dincludes n EL layers (n is a natural number of 2 or more), and theintermediate layers 207 between the EL layers.

The behaviors of electrons and holes in the intermediate layer 207provided between the EL layer 203(m) and the EL layer 203(m+1) will bedescribed. When a voltage higher than the threshold voltage of thelight-emitting element is applied between the first electrode 201 andthe second electrode 205, holes and electrons are generated in theintermediate layer 207, and the holes move into the EL layer 203(m+1)provided on the second electrode 205 side and the electrons move intothe EL layer 203(m) provided on the first electrode 201 side. The holesinjected into the EL layer 203(m+1) recombine with electrons injectedfrom the second electrode 205 side, so that a light-emitting substancecontained in the EL layer 203(m+1) emits light. Furthermore, theelectrons injected into the EL layer 203(m) recombine with holesinjected from the first electrode 201 side, so that a light-emittingsubstance contained in the EL layer 203(m) emits light. Thus, the holesand electrons generated in the intermediate layer 207 cause lightemission in different EL layers.

Note that the EL layers can be provided in contact with each other withno intermediate layer interposed therebetween when these EL layers allowthe same structure as the intermediate layer to be formed therebetween.For example, when the charge-generation region is formed over onesurface of an EL layer, another EL layer can be provided in contact withthe surface.

Furthermore, when emission colors of the EL layers are made different,light emission of a desired color can be provided from thelight-emitting element as a whole. For example, the emission colors offirst and second EL layers are complementary in a light-emitting elementhaving the two EL layers, so that the light-emitting element can be madeto emit white light as a whole. The same applies to a light-emittingelement having three or more EL layers.

<<Materials of Light-Emitting Element>>

Examples of materials which can be used for each layer will be givenbelow. Note that each layer is not limited to a single layer, and may bea stack of two or more layers.

<Anode>

The electrode serving as the anode (the first electrode 201 in thisembodiment) can be formed using one or more kinds of conductive metals,conductive alloys, conductive compounds, and the like. In particular, itis preferable to use a material with a high work function (4.0 eV ormore). The examples include indium tin oxide (ITO), indium tin oxidecontaining silicon or silicon oxide, indium zinc oxide, indium oxidecontaining tungsten oxide and zinc oxide, graphene, gold, platinum,nickel, tungsten, chromium, molybdenum, iron, cobalt, copper, palladium,titanium, and a nitride of a metal material (e.g., titanium nitride).

When the anode is in contact with the charge-generation region, any of avariety of conductive materials can be used regardless of their workfunctions; for example, aluminum, silver, an alloy containing aluminum,or the like can be used.

<Cathode>

The electrode serving as the cathode (the second electrode 205 in thisembodiment) can be formed using one or more kinds of conductive metals,conductive alloys, conductive compounds, and the like. In particular, itis preferable to use a material with a low work function (3.8 eV orless). The examples include aluminum, silver, an element belonging toGroup 1 or 2 of the periodic table (e.g., an alkali metal such aslithium or cesium, an alkaline earth metal such as calcium or strontium,or magnesium), an alloy containing any of these elements (e.g., Mg—Ag orAl—Li), a rare earth metal such as europium or ytterbium, and an alloycontaining any of these rare earth metals.

Note that when the cathode is in contact with the charge-generationregion, any of a variety of conductive materials can be used regardlessof its work function. For example, ITO or indium tin oxide containingsilicon or silicon oxide can be used.

The electrodes may be formed separately by a vacuum evaporation methodor a sputtering method. Alternatively, when a silver paste or the likeis used, a coating method or an inkjet method may be used.

<Light-Emitting Layer>

The light-emitting layer 303 contains a light-emitting substance. In anexample described in this embodiment, the light-emitting layer 303contains a guest material and a host material in which the guestmaterial is dispersed and the heterocyclic compound of one embodiment ofthe present invention is used as the host material. The heterocycliccompound of one embodiment of the present invention can be favorablyused as a host material in a light-emitting layer when a light-emittingsubstance is a phosphorescent compound emitting light in a wavelengthrange from red to green or a fluorescent compound.

When the light-emitting layer has the structure in which the guestmaterial is dispersed in the host material, the crystallization of thelight-emitting layer can be inhibited. Furthermore, it is possible toinhibit concentration quenching due to high concentration of the guestmaterial; thus, the light-emitting element can have higher emissionefficiency.

In addition to the guest material and the host material, thelight-emitting layer may contain another compound. Furthermore, inaddition to the light-emitting layer containing the heterocycliccompound of one embodiment of the present invention, the light-emittingelement of one embodiment of the present invention may include anotherlight-emitting layer. In that case, a fluorescent compound, aphosphorescent compound, or a substance emitting thermally activateddelayed fluorescence can be used as the light-emitting substance, and acompound to be described below which easily accepts electrons or acompound to be described below which easily accepts holes can be used asthe host material.

Note that it is preferable that the T₁ level of the host material (or amaterial other than the guest material in the light-emitting layer) behigher than the T₁ level of the guest material. This is because, whenthe T₁ level of the host material is lower than that of the guestmaterial, the triplet excitation energy of the guest material, which isto contribute to light emission, is quenched by the host material andaccordingly the emission efficiency is reduced.

Here, for improvement in efficiency of energy transfer from a hostmaterial to a guest material, Förster mechanism (dipole-dipoleinteraction) and Dexter mechanism (electron exchange interaction), whichare known as mechanisms of energy transfer between molecules, areconsidered. According to the mechanisms, it is preferable that anemission spectrum of a host material (fluorescence spectrum in energytransfer from a singlet excited state, phosphorescence spectrum inenergy transfer from a triplet excited state) have a large overlap withan absorption spectrum of a guest material (specifically, spectrum in anabsorption band on the longest wavelength (lowest energy) side).

However, in general, it is difficult to obtain an overlap between afluorescence spectrum of a host material and an absorption spectrum inan absorption band on the longest wavelength (lowest energy) side of aguest material. The reason for this is as follows: if the fluorescencespectrum of the host material overlaps with the absorption spectrum inthe absorption band on the longest wavelength (lowest energy) side ofthe guest material, because the phosphorescence spectrum of the hostmaterial is located on the longer wavelength (lower energy) side thanthe fluorescence spectrum, the T₁ level of the host material becomeslower than the T₁ level of the phosphorescent compound and theabove-described problem of quenching occurs; yet, when the host materialis designed in such a manner that the T₁ level of the host material ishigher than the T₁ level of the phosphorescent compound to avoid theproblem of quenching, the fluorescence spectrum of the host material isshifted to the shorter wavelength (higher energy) side, and thus thefluorescence spectrum does not have any overlap with the absorptionspectrum in the absorption band on the longest wavelength (lowestenergy) side of the guest material. For this reason, in general, it isdifficult to obtain an overlap between a fluorescence spectrum of a hostmaterial and an absorption spectrum in an absorption band on the longestwavelength (lowest energy) side of a guest material so as to maximizeenergy transfer from a singlet excited state of a host material.

Thus, it is preferable that in a light-emitting layer of alight-emitting element which uses a phosphorescent compound as a guestmaterial, a third substance be contained in addition to thephosphorescent compound and the host material (which are respectivelyregarded as a first substance and a second substance contained in thelight-emitting layer), and the host material forms an exciplex (alsoreferred to as excited complex) in combination with the third substance.In that case, the host material and the third substance form an exciplexat the time of recombination of carriers (electrons and holes) in thelight-emitting layer. Thus, in the light-emitting layer, fluorescencespectra of the host material and the third substance are converted intoan emission spectrum of the exciplex which is located on a longerwavelength side. Moreover, when the host material and the thirdsubstance are selected such that the emission spectrum of the exciplexhas a large overlap with the absorption spectrum of the guest material,energy transfer from a singlet excited state can be maximized. Note thatalso in the case of a triplet excited state, energy transfer from theexciplex, not the host material, is considered to occur. In oneembodiment of the present invention to which such a structure isapplied, energy transfer efficiency can be improved owing to energytransfer utilizing an overlap between an emission spectrum of anexciplex and an absorption spectrum of a phosphorescent compound;accordingly, a light-emitting element with high external quantumefficiency can be provided.

As the guest material, a phosphorescent compound to be described belowcan be used. Although any combination of the host material and the thirdsubstance can be used as long as an exciplex is formed, a compound whicheasily accepts electrons (a compound having an electron-trappingproperty) and a compound which easily accepts holes (a compound having ahole-trapping property) are preferably combined. The heterocycliccompound of one embodiment of the present invention can be used as acompound having an electron-trapping property.

Thus, the light-emitting element of one embodiment of the presentinvention includes, between a pair of electrodes, a light-emitting layercontaining a phosphorescent compound emitting light in a wavelengthrange from red to green, the heterocyclic compound of one embodiment ofthe present invention, and a compound which easily accepts holes.

Examples of a compound which easily accepts holes and which can be usedas the host material or the third substance are a n-electron richheteroaromatic compound (e.g., a carbazole derivative or an indolederivative) and an aromatic amine compound.

Specifically, the following examples can be given:N-(1,1′-biphenyl-4-yl)-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-9,9-dimethyl-9H-fluoren-2-amine (abbreviation: PCBBiF),4-phenyl-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation:PCBA1BP),4,4′-di(1-naphthyl)-4″-(9-phenyl-9H-carbazol-3-yl)triphenylamine(abbreviation: PCBNBB),3-[N-(1-naphthyl)-N-(9-phenylcarbazol-3-yl)amino]-9-phenylcarbazole(abbreviation: PCzPCN1),4,4′,4″-tris[N-(1-naphthyl)-N-phenylamino]triphenylamine (abbreviation:1′-TNATA),2,7-bis[N-(4-diphenylaminophenyl)-N-phenylamino]spiro-9,9′-bifluorene(abbreviation: DPA2SF),N,N′-bis(9-phenylcarbazol-3-yl)-N,N′-diphenylbenzene-1,3-diamine(abbreviation: PCA2B),N-(9,9-dimethyl-2-diphenylamino-9H-fluoren-7-yl)diphenylamine(abbreviation: DPNF),N,N,N′-triphenyl-N,N,N′-tris(9-phenylcarbazol-3-yl)benzene-1,3,5-triamine(abbreviation: PCA3B),2-[N-(9-phenylcarbazol-3-yl)-N-phenylamino]spiro-9,9′-bifluorene(abbreviation: PCASF),2-[N-(4-diphenylaminophenyl)-N-phenylamino]spiro-9,9′-bifluorene(abbreviation: DPASF),N,N′-bis[4-(carbazol-9-yl)phenyl]-N,N-diphenyl-9,9-dimethylfluorene-2,7-diamine(abbreviation: YGA2F),N,N-bis(3-methylphenyl)-N,N′-diphenyl-[1,1′-biphenyl]-4,4′-diamine(abbreviation: TPD),4,4′-bis[N-(4-diphenylaminophenyl)-N-phenylamino]biphenyl (abbreviation:DPAB),N-(9,9-dimethyl-9H-fluoren-2-yl)-N-{9,9-dimethyl-2-[N-phenyl-N′-(9,9-dimethyl-9H-fluoren-2-yl)amino]-9H-fluoren-7-yl}phenylamine (abbreviation: DFLADFL),3-[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzPCA1),3,6-bis[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzPCA2),3-[N-(4-diphenylaminophenyl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzDPA1),3,6-bis[N-(4-diphenylaminophenyl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzDPA2),4,4′-bis(N-{4-[N-(3-methylphenyl)-N-phenylamino]phenyl}-N-phenylamino)biphenyl(abbreviation: DNTPD),3,6-bis[N-(4-diphenylaminophenyl)-N-(1-naphthyl)amino]-9-phenylcarbazole(abbreviation: PCzTPN2), and the like.

The following examples can also be given: aromatic amine compounds suchas 4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB orα-NPD), 4,4′,4″-tris(N,N-diphenylamino)triphenylamine (abbreviation:TDATA), 4,4′,4″-tris[N-(3-methylphenyl)-N-phenylamino]triphenylamine(abbreviation: MTDATA),4,4′-bis[N-(spiro-9,9′-bifluoren-2-yl)-N-phenylamino]biphenyl(abbreviation: BSPB), 4,4′,4″-tris(N-carbazolyl)triphenylamine(abbreviation: TCTA), 4-phenyl-4′-(9-phenylfluoren-9-yl)triphenylamine(abbreviation: BPAFLP), and4,4′-bis[N-(9,9-dimethylfluoren-2-yl)-N-phenylamino]biphenyl(abbreviation: DFLDPBi); and carbazole derivatives such as4,4′-di(N-carbazolyl)biphenyl (abbreviation: CBP),9-[4-(10-phenyl-9-anthracenyl)phenyl]-9H-carbazole (abbreviation: CzPA),and 9-phenyl-3-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole(abbreviation: PCzPA). In addition, high molecular compounds such aspoly(N-vinylcarbazole) (abbreviation: PVK), poly(4-vinyltriphenylamine)(abbreviation: PVTPA),poly[N-(4-{N-[4-(4-diphenylamino)phenyl]phenyl-N-phenylamino}phenyl)methacrylamide] (abbreviation: PTPDMA), andpoly[N,N′-bis(4-butylphenyl)-N,N-bis(phenyl)benzidine] (abbreviation:Poly-TPD) can be given.

Examples of the compound which easily accepts electrons and which can beused as the host material or the third substance include theheterocyclic compound of one embodiment of the present invention, art-electron deficient heteroaromatic compound such as anitrogen-containing heteroaromatic compound, a metal complex having aquinoline skeleton or a benzoquinoline skeleton, and a metal complexhaving an oxazole-based ligand or a thiazole-based ligand.

Specific examples include the following: metal complexes such asbis(10-hydroxybenzo[h]quinolinato)beryllium (abbreviation: BeBq₂),bis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum (abbreviation:BAlq), bis(8-quinolinolato)zinc(II) (abbreviation: Znq),bis[2-(2-hydroxyphenyl)benzoxazolato]zinc (abbreviation: Zn(BOX)₂), andbis[2-(2-hydroxyphenyl)benzothiazolato]zinc (abbreviation: Zn(BTZ)₂);heterocyclic compounds having polyazole skeletons, such as2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (abbreviation:PBD), 3-(4-biphenylyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole(abbreviation: TAZ),1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene(abbreviation: OXD-7),9-[4-(5-phenyl-1,3,4-oxadiazol-2-yl)phenyl]-9H-carbazole (abbreviation:CO11), 2,2′,2″-(1,3,5-benzenetriyl)tris(1-phenyl-1H-benzimidazole)(abbreviation: TPBI), and2-[3-(dibenzothiophen-4-yl)phenyl]-1-phenyl-1H-benzimidazole(abbreviation: mDBTBIm-II); heterocyclic compounds having quinoxalineskeletons or dibenzoquinoxaline skeletons, such as2-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation:2mDBTPDBq-II),2-[3′-(dibenzothiophen-4-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline(abbreviation: 2mDBTBPDBq-II),2-[4-(3,6-diphenyl-9H-carbazol-9-yl)phenyl]dibenzo[f,h]quinoxaline(abbreviation: 2CzPDBq-III),7-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation:7mDBTPDBq-II), 6-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline(abbreviation: 6mDBTPDBq-II), and2-[3′-(9H-carbazol-9-yl)biphenyl-3-yl]dibenzo[1h]quinoxaline(abbreviation: 2mCzBPDBq); heterocyclic compounds having diazineskeletons (pyrimidine skeletons or pyrazine skeletons), such as4,6-bis[3-(phenanthren-9-yl)phenyl]pyrimidine (abbreviation:4,6mPnP2Pm), 4,6-bis[3-(9H-carbazol-9-yl)phenyl]pyrimidine(abbreviation: 4,6mCzP2Pm), and4,6-bis[3-(4-dibenzothienyl)phenyl]pyrimidine (abbreviation:4,6mDBTP2Pm-II); heterocyclic compounds having pyridine skeletons, suchas 3,5-bis[3-(9H-carbazol-9-yl)phenyl]pyridine (abbreviation:3,5DCzPPy), 1,3,5-tri[3-(3-pyridyl)phenyl]benzene (abbreviation:TmPyPB), and 3,3′,5,5′-tetra[(m-pyridyl)-phen-3-yl]biphenyl(abbreviation: BP4mPy). Among the above materials, heterocycliccompounds having quinoxaline skeletons or dibenzoquinoxaline skeletons,heterocyclic compounds having diazine skeletons, and heterocycliccompounds having pyridine skeletons are preferable because of their highreliability.

The following examples can also be given: metal complexes havingquinoline skeletons or benzoquinoline skeletons, such astris(8-quinolinolato)aluminum (abbreviation: Alq) andtris(4-methyl-8-quinolinolato)aluminum (abbreviation: Almq₃); andheteroaromatic compounds such as bathophenanthroline (abbreviation:BPhen), bathocuproine (abbreviation: BCP),3-(4-tert-butylphenyl)-4-(4-ethylphenyl)-5-(4-biphenylyl)-1,2,4-triazole(abbreviation: p-EtTAZ), and 4,4′-bis(5-methylbenzoxazol-2-yl)stilbene(abbreviation: BzOs). In addition, high molecular compounds such aspoly(2,5-pyridinediyl) (abbreviation: PPy),poly[(9,9-dihexylfluorene-2,7-diyl)-co-(pyridine-3,5-diyl)](abbreviation: PF-Py), andpoly[(9,9-dioctylfluorene-2,7-diyl)-co-(2,2′-bipyridine-6,6′-diyl)](abbreviation: PF-BPy) can also be given.

The materials which can be used as the host material or the thirdsubstance are not limited to the above materials as long as the materialused as the host material forms an exciplex in combination with thematerial used as the third substance, an emission spectrum of theexciplex overlaps with an absorption spectrum of the guest material, anda peak of the emission spectrum of the exciplex is located on a longerwavelength side than a peak of the absorption spectrum of the guestmaterial.

Note that when a compound which easily accepts electrons and a compoundwhich easily accepts holes are used for the host material and the thirdsubstance, carrier balance can be controlled by the mixture ratio of thecompounds. Specifically, the ratio of the host material to the thirdsubstance is preferably from 1:9 to 9:1.

Furthermore, the exciplex may be formed at the interface between twolayers. For example, when a layer containing the compound which easilyaccepts electrons and a layer containing the compound which easilyaccepts holes are stacked, the exciplex is formed in the vicinity of theinterface thereof. These two layers may be used as the light-emittinglayer in the light-emitting element of one embodiment of the presentinvention. In that case, the phosphorescent compound may be added to thevicinity of the interface. The phosphorescent compound may be added toone of the two layers or both.

<<Guest Material>>

Examples of fluorescent compounds that can be used for thelight-emitting layer 303 are given. Examples of materials that emit bluelight are as follows:N,N-bis(3-methylphenyl)-N,N-bis[3-(9-phenyl-9H-fluoren-9-yl)phenyl]pyrene-1,6-diamine (abbreviation: 1,6mMemFLPAPrn),N,N-bis(dibenzofuran-4-yl)-N,N-diphenylpyrene-1,6-diamine (abbreviation:1,6FrAPrn-II),N,N-bis[4-(9H-carbazol-9-yl)phenyl]-N,N-diphenylstilbene-4,4′-diamine(abbreviation: YGA2S),4-(9H-carbazol-9-yl)-4′-(10-phenyl-9-anthryl)triphenylamine(abbreviation: YGAPA), and4-(10-phenyl-9-anthryl)-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine(abbreviation: PCBAPA). Examples of materials that emit green light areas follows: N-(9,10-diphenyl-2-anthryl)-N,9-diphenyl-9H-carbazol-3-amine(abbreviation: 2PCAPA),N-[9,10-bis(1,1′-biphenyl-2-yl)-2-anthryl]-N,9-diphenyl-9H-carbazol-3-amine(abbreviation: 2PCABPhA),N-(9,10-diphenyl-2-anthryl)-N,N,N-triphenyl-1,4-phenylenediamine(abbreviation: 2DPAPA),N-[9,10-bis(1,1′-biphenyl-2-yl)-2-anthryl]-N,N,N-triphenyl-1,4-phenylenediamine(abbreviation: 2DPABPhA),9,10-bis(1,1′-biphenyl-2-yl)-N-[4-(9H-carbazol-9-yl)phenyl]-N-phenylanthracen-2-amine(abbreviation: 2YGABPhA), and N,N,9-triphenylanthracen-9-amine(abbreviation: DPhAPhA). Examples of materials that emit yellow lightare as follows: rubrene and5,12-bis(1,1′-biphenyl-4-yl)-6,11-diphenyltetracene (abbreviation: BPT).Examples of materials that emit red light are as follows:N,N,N,N-tetrakis(4-methylphenyl)tetracene-5,11-diamine (abbreviation:p-mPhTD) and7,14-diphenyl-N,N,N,N-tetrakis(4-methylphenyl)acenaphtho[1,2-α]fluoranthene-3,10-diamine(abbreviation: p-mPhAFD).

Examples of phosphorescent compounds that can be used for thelight-emitting layer 303 are given. For example, a phosphorescentcompound having an emission peak at 440 nm to 520 nm is given, examplesof which include organometallic iridium complexes having 4H-triazoleskeletons, such as tris{2-[5-(2-methylphenyl)-4-(2,6-dimethylphenyl)-4H-1,2,4-triazol-3-yl-KN2]phenyl-KC} iridium(III) (abbreviation: [Ir(mpptz-dmp)₃]),tris(5-methyl-3,4-diphenyl-4H-1,2,4-triazolato)iridium(III)(abbreviation: [Ir(Mptz)₃]), andtris[4-(3-biphenyl)-5-isopropyl-3-phenyl-4H-1,2,4-triazolato]iridium(III)(abbreviation: [Ir(iPrptz-3b)₃]); organometallic iridium complexeshaving 1H-triazole skeletons, such astris[3-methyl-1-(2-methylphenyl)-5-phenyl-1H-1,2,4-triazolato]iridium(III)(abbreviation: [Ir(Mptz-mp)₃]) andtris(1-methyl-5-phenyl-3-propyl-1H-1,2,4-triazolato)iridium(III)(abbreviation: [Ir(Prptz1-Me)₃]); organometallic iridium complexeshaving imidazole skeletons, such asfac-tris[1-(2,6-diisopropylphenyl)-2-phenyl-1H-imidazole]iridium(III)(abbreviation: [Ir(iPrpmi)₃]) andtris[3-(2,6-dimethylphenyl)-7-methylimidazo[1,2-f]phenanthridinato]iridium(III)(abbreviation: [Ir(dmpimpt-Me)₃]); and organometallic iridium complexesin which a phenylpyridine derivative having an electron-withdrawinggroup is a ligand, such asbis[2-(4′,6′-difluorophenyl)pyridinato-N,C^(2′)]iridium(III)tetrakis(1-pyrazolyl)borate (abbreviation: FIr6),bis[2-(4′,6′-difluorophenyl)pyridinato-N,C^(2′)]iridium(III) picolinate(abbreviation: FIrpic), bis{2-[3′,5′-bis(trifluoromethyl)phenyl]pyridinato-N, C²}iridium(III)picolinate (abbreviation: [Ir(CF₃ppy)₂(pic)]), andbis[2-(4′,6′-difluorophenyl)pyridinato-N, C^(2′)]iridium(III)acetylacetonate (abbreviation: FIracac). Among the materials givenabove, the organometallic iridium complexes having 4H-triazole skeletonshave high reliability and high emission efficiency and are thusespecially preferable.

Examples of the phosphorescent compound having an emission peak at 520nm to 600 nm include organometallic iridium complexes having pyrimidineskeletons, such as tris(4-methyl-6-phenylpyrimidinato)iridium(III)(abbreviation: [Ir(mppm)₃]),tris(4-t-butyl-6-phenylpyrimidinato)iridium(III) (abbreviation:[Ir(tBuppm)₃]),(acetylacetonato)bis(6-methyl-4-phenylpyrimidinato)iridium(III)(abbreviation: [Ir(mppm)₂(acac)]),(acetylacetonato)bis(6-tert-butyl-4-phenylpyrimidinato)iridium(III)(abbreviation: [Ir(tBuppm)₂(acac)]),(acetylacetonato)bis[4-(2-norbornyl)-6-phenylpyrimidinato]iridium(III)(endo- and exo-mixture) (abbreviation: [Ir(nbppm)₂(acac)]),(acetylacetonato)bis[5-methyl-6-(2-methylphenyl)-4-phenylpyrimidinato]iridium(III)(abbreviation: [Ir(mpmppm)₂(acac)]), and(acetylacetonato)bis(4,6-diphenylpyrimidinato)iridium(III)(abbreviation: [Ir(dppm)₂(acac)]); organometallic iridium complexeshaving pyrazine skeletons, such as(acetylacetonato)bis(3,5-dimethyl-2-phenylpyrazinato)iridium(III)(abbreviation: [Ir(mppr-Me)₂(acac)]) and(acetylacetonato)bis(5-isopropyl-3-methyl-2-phenylpyrazinato)iridium(III)(abbreviation: [Ir(mppr-iPr)₂(acac)]); organometallic iridium complexeshaving pyridine skeletons, such astris(2-phenylpyridinato-N,C^(2′))iridium(III) (abbreviation:[Ir(ppy)₃]), bis(2-phenylpyridinato-N,C^(2′))iridium(III)acetylacetonate (abbreviation: [Ir(ppy)₂(acac)]),bis(benzo[h]quinolinato)iridium(III) acetylacetonate (abbreviation:[Ir(bzq)₂(acac)]), tris(benzo[h]quinolinato)iridium(III) (abbreviation:[Ir(bzq)₃]), tris(2-phenylquinolinato-N,C^(2′))iridium(III)(abbreviation: [Ir(pq)₃]), andbis(2-phenylquinolinato-N,C^(2′))iridium(III) acetylacetonate(abbreviation: [Ir(pq)₂(acac)]); and a rare earth metal complex such astris(acetylacetonato)(monophenanthroline)terbium(III) (abbreviation:[Tb(acac)₃(Phen)]). Among the above materials, the organometalliciridium complexes having pyrimidine skeletons are particularlypreferable because of their distinctively high reliability and emissionefficiency.

Examples of the phosphorescent compound having an emission peak at 600nm to 700 nm include organometallic iridium complexes having pyrimidineskeletons, such as(diisobutyrylmethanato)bis[4,6-bis(3-methylphenyl)pyrimidinato]iridium(III)(abbreviation: [Ir(5mdppm)₂(dibm)]),bis[4,6-bis(3-methylphenyl)pyrimidinato](dipivaloylmethanato)iridium(III)(abbreviation: [Ir(5mdppm)₂(dpm)]), andbis[4,6-di(naphthalen-1-yl)pyrimidinato](dipivaloylmethanato)iridium(III)(abbreviation: [Ir(dlnpm)₂(dpm)]); organometallic iridium complexeshaving pyrazine skeletons, such as(acetylacetonato)bis(2,3,5-triphenylpyrazinato)iridium(III)(abbreviation: [Ir(tppr)₂(acac)]), bis(2,3,5-triphenylpyrazinato)(dipivaloylmethanato)iridium(III) (abbreviation:[Ir(tppr)₂(dpm)]), and(acetylacetonato)bis[2,3-bis(4-fluorophenyl)quinoxalinato]iridium(III)(abbreviation: [Ir(Fdpq)₂(acac)]); organometallic iridium complexeshaving pyridine skeletons, such astris(1-phenylisoquinolinato-N,C^(2′))iridium(III) (abbreviation:[Ir(piq)₃]) andbis(1-phenylisoquinolinato-N,C^(2′))iridium(III)acetylacetonate(abbreviation: [Ir(piq)₂(acac)]); a platinum complex such as 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyrin platinum(II) (abbreviation:PtOEP); and rare earth metal complexes such astris(1,3-diphenyl-1,3-propanedionato) (monophenanthroline)europium(III)(abbreviation: [Eu(DBM)₃(Phen)]) andtris[1-(2-thenoyl)-3,3,3-trifluoroacetonato](monophenanthroline)europium(III)(abbreviation: [Eu(TTA)₃(Phen)]). Among the materials given above, theorganometallic iridium complexes having pyrimidine skeletons havedistinctively high reliability and emission efficiency and are thusespecially preferable. Furthermore, the organometallic iridium complexeshaving pyrazine skeletons can provide red light emission with favorablechromaticity.

Alternatively, a high molecular compound can be used for thelight-emitting layer 303. Examples of the materials that emit blue lightinclude poly(9,9-dioctylfluorene-2,7-diyl) (abbreviation: POF),poly[(9,9-dioctylfluorene-2,7-diyl-co-(2,5-dimethoxybenzene-1,4-diyl)](abbreviation: PF-DMOP), andpoly{(9,9-dioctylfluorene-2,7-diyl)-co-[N,N-di-(p-butylphenyl)-1,4-diaminobenzene]}(abbreviation:TAB-PFH). Examples of the materials that emit green light includepoly(p-phenylenevinylene) (abbreviation: PPV),poly[(9,9-dihexylfluorene-2,7-diyl)-alt-co-(benzo[2,1,3]thiadiazole-4,7-diyl)](abbreviation:PFBT), andpoly[(9,9-dioctyl-2,7-divinylenefluorenylene)-alt-co-(2-methoxy-5-(2-ethylheloxy)-1,4-phenylene)].Examples of the materials that emit orange to red light includepoly[2-methoxy-5-(2-ethylhexoxy)-1,4-phenylenevinylene] (abbreviation:MEH-PPV), poly(3-butylthiophene-2,5-diyl), poly{[9,9-dihexyl-2,7-bis(1-cyanovinylene)fluorenylene]-alt-co-[2,5-bis(N,N-diphenylamino)-1,4-phenylene]},andpoly{[2-methoxy-5-(2-ethylhexyloxy)-1,4-bis(1-cyanovinylenephenylene)]-alt-co-[2,5-bis(N,N-diphenylamino)-1,4-phenylene]}(abbreviation: CN-PPV-DPD).

<Hole-Transport Layer>

The hole-transport layer 302 contains a substance with a highhole-transport property.

The substance with a high hole-transport property is a substance havinga hole-transport property higher than an electron-transport property,and is especially preferably a substance with a hole mobility of 10⁻⁶cm²/Vs or more.

For the hole-transport layer 302, it is possible to use any of thecompounds which easily accept holes and are described as examples of thesubstance applicable to the light-emitting layer 303.

It is also possible to use an aromatic hydrocarbon compound such as2-tert-butyl-9,10-di(2-naphthyl)anthracene (abbreviation: t-BuDNA),9,10-di(2-naphthyl)anthracene (abbreviation: DNA), or9,10-diphenylanthracene (abbreviation: DPAnth).

<Electron-Transport Layer>

The electron-transport layer 304 contains a substance with a highelectron-transport property.

The substance with a high electron-transport property is an organiccompound having an electron-transport property higher than ahole-transport property, and is especially preferably a substance withan electron mobility of 10⁻⁶ cm²/Vs or more.

For the electron-transport layer 304, it is possible to use any of thecompounds which easily accept electrons and are described as examples ofthe substance applicable to the light-emitting layer 303.

<Hole-Injection Layer>

The hole-injection layer 301 contains a substance with a highhole-injection property.

Examples of the substance with a high hole-injection property includemetal oxides such as molybdenum oxide, titanium oxide, vanadium oxide,rhenium oxide, ruthenium oxide, chromium oxide, zirconium oxide, hafniumoxide, tantalum oxide, silver oxide, tungsten oxide, and manganeseoxide.

Alternatively, it is possible to use a phthalocyanine-based compoundsuch as phthalocyanine (abbreviation: H₂Pc) or copper(II) phthalocyanine(abbreviation: CuPc).

Further alternatively, it is possible to use an aromatic amine compoundwhich is a low molecular organic compound, such as TDATA, MTDATA, DPAB,DNTPD, 1,3,5-tris[N-(4-diphenylaminophenyl)-N-phenylamino]benzene(abbreviation: DPA3B), PCzPCA1, PCzPCA2, or PCzPCN1.

Further alternatively, it is possible to use a high molecular compoundsuch as PVK, PVTPA, PTPDMA, or Poly-TPD, or a high molecular compound towhich acid is added, such aspoly(3,4-ethylenedioxythiophene)/poly(styrenesulfonic acid) (PEDOT/PSS)or polyaniline/poly(styrenesulfonic acid) (PAni/PSS).

The hole-injection layer 301 may serve as the charge-generation region.When the hole-injection layer 301 in contact with the anode serves asthe charge-generation region, any of a variety of conductive materialscan be used for the anode regardless of their work functions. Materialscontained in the charge-generation region will be described below.

<Electron-Injection Layer>

The electron-injection layer 305 contains a substance with a highelectron-injection property.

Examples of the substance with a high electron-injection propertyinclude an alkali metal, an alkaline earth metal, a rare earth metal,and a compound thereof (e.g., an oxide thereof, a carbonate thereof, anda halide thereof), such as lithium, cesium, calcium, lithium oxide,lithium carbonate, cesium carbonate, lithium fluoride, cesium fluoride,calcium fluoride, and erbium fluoride. Electride can also be used. As anexample of electride, a substance in which electrons are added at highconcentration to an oxide containing calcium and aluminum.

The electron-injection layer 305 may serve as the charge-generationregion. When the electron-injection layer 305 in contact with thecathode serves as the charge-generation region, any of a variety ofconductive materials can be used for the cathode regardless of theirwork functions. Materials contained in the charge-generation region willbe described below.

<Charge-Generation Region>

The charge-generation region may have either a structure in which anelectron acceptor (acceptor) is added to an organic compound with a highhole-transport property or a structure in which an electron donor(donor) is added to an organic compound with a high electron-transportproperty. Alternatively, these structures may be stacked.

As examples of an organic compound with a high hole-transport property,the above materials which can be used for the hole-transport layer canbe given, and as examples of an organic compound with a highelectron-transport property, the above materials which can be used forthe electron-transport layer can be given.

Furthermore, as the electron acceptor,7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane (abbreviation:F₄-TCNQ), chloranil, and the like can be given. In addition, atransition metal oxide can be given. In addition, an oxide of metalsthat belong to Group 4 to Group 8 of the periodic table can be given.Specifically, vanadium oxide, niobium oxide, tantalum oxide, chromiumoxide, molybdenum oxide, tungsten oxide, manganese oxide, and rheniumoxide are preferable because of their high electron-acceptingproperties. Among these, molybdenum oxide is especially preferable sinceit is stable in the air, has a low hygroscopic property, and is easy tohandle.

Furthermore, as the electron donor, it is possible to use an alkalimetal, an alkaline earth metal, a rare earth metal, a metal belonging toGroup 2 or Group 13 of the periodic table, or an oxide or a carbonatethereof. Specifically, lithium, cesium, magnesium, calcium, ytterbium,indium, lithium oxide, cesium carbonate, or the like is preferably used.Alternatively, an organic compound such as tetrathianaphthacene may beused as the electron donor.

The above-described layers included in the EL layer 203 and theintermediate layer 207 can be formed separately by any of the followingmethods: an evaporation method (including a vacuum evaporation method),a transfer method, a printing method, an inkjet method, a coatingmethod, and the like.

This embodiment can be freely combined with any of other embodiments.

Embodiment 3

In this embodiment, a light-emitting device of one embodiment of thepresent invention will be described with reference to FIGS. 2A and 2Band FIGS. 3A to 3C. The light-emitting device of this embodimentincludes the light-emitting element of one embodiment of the presentinvention. Since the light-emitting element has a long lifetime, alight-emitting device having high reliability can be provided.

FIG. 2A is a plan view of a light-emitting device of one embodiment ofthe present invention, and FIG. 2B is a cross-sectional view taken alongdashed-dotted line A-B in FIG. 2A.

In the light-emitting device of this embodiment, a light-emittingelement 403 is provided in a space 415 surrounded by a support substrate401, a sealing substrate 405, and a sealing material 407. Thelight-emitting element 403 is an organic EL element having abottom-emission structure; specifically, a first electrode 421 whichtransmits visible light is provided over the support substrate 401, anEL layer 423 is provided over the first electrode 421, and a secondelectrode 425 which reflects visible light is provided over the EL layer423. The EL layer 423 contains the heterocyclic compound of oneembodiment of the present invention which is described in Embodiment 1.

A first terminal 409 a is electrically connected to an auxiliary wiring417 and the first electrode 421. An insulating layer 419 is providedover the first electrode 421 in a region which overlaps with theauxiliary wiring 417. The first terminal 409 a is electrically insulatedfrom the second electrode 425 by the insulating layer 419. A secondterminal 409 b is electrically connected to the second electrode 425.Note that although the first electrode 421 is formed over the auxiliarywiring 417 in this embodiment, the auxiliary wiring 417 may be formedover the first electrode 421.

A light extraction structure 411 a is preferably provided at theinterface between the support substrate 401 and the atmosphere. Whenprovided at the interface between the support substrate 401 and theatmosphere, the light extraction structure 411 a can reduce light thatcannot be extracted to the atmosphere because of total reflection,resulting in an increase in the light extraction efficiency of thelight-emitting device.

In addition, a light extraction structure 411 b is preferably providedat the interface between the light-emitting element 403 and the supportsubstrate 401. When the light extraction structure 411 b has unevenness,a planarization layer 413 is preferably provided between the lightextraction structure 411 b and the first electrode 421. Accordingly, thefirst electrode 421 can be a flat film, and generation of leakagecurrent in the EL layer 423 due to the unevenness of the first electrode421 can be prevented. Furthermore, because of the light extractionstructure 411 b at the interface between the planarization layer 413 andthe support substrate 401, light that cannot be extracted to theatmosphere because of total reflection can be reduced, so that the lightextraction efficiency of the light-emitting device can be increased.

As a material of the light extraction structure 411 a and the lightextraction structure 411 b, a resin can be used, for example.Alternatively, for the light extraction structure 411 a and the lightextraction structure 411 b, a hemispherical lens, a micro lens array, afilm provided with an uneven surface structure, a light diffusing film,or the like can be used. For example, the light extraction structure 411a and the light extraction structure 411 b can be formed by attachingthe lens or film to the support substrate 401 with an adhesive or thelike which has substantially the same refractive index as the supportsubstrate 401 or the lens or film.

The surface of the planarization layer 413 which is in contact with thefirst electrode 421 is flatter than the surface of the planarizationlayer 413 which is in contact with the light extraction structure 411 b.As a material of the planarization layer 413, glass, liquid, a resin, orthe like having a light-transmitting property and a high refractiveindex can be used.

FIG. 3A is a plan view of a light-emitting device of one embodiment ofthe present invention, FIG. 3B is a cross-sectional view taken alongdashed-dotted line C-D in FIG. 3A, and FIG. 3C is a cross-sectional viewillustrating a modified example of the light-emitting portion.

An active matrix light-emitting device of this embodiment includes, overa support substrate 501, a light-emitting portion 551 (the cross sectionof which is illustrated in FIG. 3B and FIG. 3C as a light-emittingportion 551 a and a light-emitting portion 551 b, respectively), adriver circuit portion 552 (gate side driver circuit portion), a drivercircuit portion 553 (source side driver circuit portion), and a sealingmaterial 507. The light-emitting portion 551 and the driver circuitportions 552 and 553 are sealed in a space 515 surrounded by the supportsubstrate 501, a sealing substrate 505, and the sealing material 507.

Any of a separate coloring method, a color filter method, and a colorconversion method can be applied to the light-emitting device of oneembodiment of the present invention. The light-emitting portion 551 afabricated by a color filter method is illustrated in FIG. 3B, and thelight-emitting portion 551 b fabricated by a separate coloring method isillustrated in FIG. 3C.

Each of the light-emitting portion 551 a and the light-emitting portion551 b includes a plurality of light-emitting units each including aswitching transistor 541 a, a current control transistor 541 b, and asecond electrode 525 electrically connected to a wiring (a sourceelectrode or a drain electrode) of the current control transistor 541 b.

A light-emitting element 503 included in the light-emitting portion 551a has a bottom-emission structure and includes a first electrode 521which transmits visible light, an EL layer 523, and the second electrode525. Furthermore, a partition 519 is formed so as to cover an endportion of the first electrode 521.

A light-emitting element 504 included in the light-emitting portion 551b has a top-emission structure and includes a first electrode 561, an ELlayer 563, and the second electrode 565 which transmits visible light.Furthermore, the partition 519 is formed so as to cover an end portionof the first electrode 561. In the EL layer 563, at least layers (e.g.,light-emitting layers) which contain a variable material depending onthe light-emitting element are colored separately.

Over the support substrate 501, a lead wiring 517 for connecting anexternal input terminal through which a signal (e.g., a video signal, aclock signal, a start signal, or a reset signal) or a potential from theoutside is transmitted to the driver circuit portion 552 or 553 isprovided. Here, an example is described in which a flexible printedcircuit (FPC) 509 is provided as the external input terminal.

The driver circuit portions 552 and 553 include a plurality oftransistors. FIG. 3B illustrates two of the transistors in the drivercircuit portion 552 (transistors 542 and 543).

To prevent an increase in the number of manufacturing steps, the leadwiring 517 is preferably formed using the same material and the samestep(s) as those of the electrode or the wiring in the light-emittingportion or the driver circuit portion. Described in this embodiment isan example in which the lead wiring 517 is formed using the samematerial and the same step(s) as those of the source electrodes and thedrain electrodes of the transistors included in the light-emittingportion 551 and the driver circuit portion 552.

In FIG. 3B, the sealing material 507 is in contact with a firstinsulating layer 511 over the lead wiring 517. The adhesion of thesealing material 507 to metal is low in some cases. Therefore, thesealing material 507 is preferably in contact with an inorganicinsulating film over the lead wiring 517. Such a structure enables alight-emitting device to have high sealing capability, high adhesion,and high reliability. Examples of the inorganic insulating film includeoxide films of metals and semiconductors, nitride films of metals andsemiconductors, and oxynitride films of metals and semiconductors, andspecifically, a silicon oxide film, a silicon nitride film, a siliconoxynitride film, a silicon nitride oxide film, an aluminum oxide film, atitanium oxide film, and the like.

The first insulating layer 511 has an effect of preventing diffusion ofimpurities into a semiconductor included in the transistor. As thesecond insulating layer 513, an insulating film having a planarizationfunction is preferably selected in order to reduce surface unevennessdue to the transistor.

There is no particular limitation on the structure and materials of thetransistor used in the light-emitting device of one embodiment of thepresent invention. A top-gate transistor may be used, or a bottom-gatetransistor such as an inverted staggered transistor may be used. Thetransistor may be a channel-etched transistor or a channel-protectivetransistor. An n-channel transistor may be used and a p-channeltransistor may also be used.

A semiconductor layer can be formed using silicon or an oxidesemiconductor. It is preferable that the transistor be formed using anoxide semiconductor which is an In—Ga—Zn-based metal oxide for asemiconductor layer so as to have low off-state current because anoff-state leakage current of the light-emitting element can be reduced.

The sealing substrate 505 illustrated in FIG. 3B is provided with acolor filter 533 as a coloring layer at a position overlapping with thelight-emitting element 503 (a light-emitting region thereof), and isalso provided with a black matrix 531 at a position overlapping with thepartition 519. Furthermore, an overcoat layer 535 is provided so as tocover the color filter 533 and the black matrix 531. The sealingsubstrate 505 illustrated in FIG. 3C is provided with a desiccant 506.

This embodiment can be combined with any other embodiment asappropriate.

Embodiment 4

In this embodiment, examples of electronic devices and lighting devicesto which the light-emitting device of one embodiment of the presentinvention is applied will be described with reference to FIGS. 4A to 4Eand FIGS. 5A and 5B.

Electronic devices of this embodiment each include the light-emittingdevice of one embodiment of the present invention in a display portion.Lighting devices of this embodiment each include the light-emittingdevice of one embodiment of the present invention in a light-emittingportion (a lighting portion). Highly reliable electronic devices andhighly reliable lighting devices can be provided by adopting thelight-emitting device of one embodiment of the present invention.

Examples of electronic devices to which the light-emitting device isapplied are television devices (also referred to as TV or televisionreceivers), monitors for computers and the like, cameras such as digitalcameras and digital video cameras, digital photo frames, cellular phones(also referred to as mobile phones or portable telephone devices),portable game machines, portable information terminals, audio playbackdevices, large game machines such as pin-ball machines, and the like.Specific examples of these electronic devices and lighting devices areillustrated in FIGS. 4A to 4E and FIGS. 5A and 5B.

FIG. 4A illustrates an example of a television device. In a televisiondevice 7100, a display portion 7102 is incorporated in a housing 7101.The display portion 7102 is capable of displaying images. Thelight-emitting device of one embodiment of the present invention can beused for the display portion 7102. In addition, here, the housing 7101is supported by a stand 7103.

The television device 7100 can be operated with an operation switchprovided in the housing 7101 or a separate remote controller 7111. Withoperation keys of the remote controller 7111, channels and volume can becontrolled and images displayed on the display portion 7102 can becontrolled. The remote controller 7111 may be provided with a displayportion for displaying data output from the remote controller 7111.

Note that the television device 7100 is provided with a receiver, amodem, and the like. With the use of the receiver, general televisionbroadcasting can be received. Moreover, when the television device isconnected to a communication network with or without wires via themodem, one-way (from a sender to a receiver) or two-way (between asender and a receiver or between receivers) information communicationcan be performed.

FIG. 4B illustrates an example of a computer. A computer 7200 includes amain body 7201, a housing 7202, a display portion 7203, a keyboard 7204,an external connection port 7205, a pointing device 7206, and the like.Note that this computer is manufactured by using the light-emittingdevice of one embodiment of the present invention for the displayportion 7203.

FIG. 4C illustrates an example of a portable game machine. A portablegame machine 7300 has two housings, a housing 7301 a and a housing 7301b, which are connected with a joint portion 7302 so that the portablegame machine can be opened or closed. The housing 7301 a incorporates adisplay portion 7303 a, and the housing 7301 b incorporates a displayportion 7303 b. In addition, the portable game machine illustrated inFIG. 4C includes a speaker portion 7304, a recording medium insertionportion 7305, an operation key 7306, a connection terminal 7307, asensor 7308 (a sensor having a function of measuring or sensing force,displacement, position, speed, acceleration, angular velocity,rotational frequency, distance, light, liquid, magnetism, temperature,chemical substance, sound, time, hardness, electric field, electriccurrent, voltage, electric power, radiation, flow rate, humidity,gradient, oscillation, odor, or infrared rays), an LED lamp, amicrophone, and the like. It is needless to say that the structure ofthe portable game machine is not limited to the above structure as longas the light-emitting device of one embodiment of the present inventionis used for at least either the display portion 7303 a or the displayportion 7303 b, or both, and may include other accessories asappropriate. The portable game machine illustrated in FIG. 4C has afunction of reading out a program or data stored in a recoding medium todisplay it on the display portion, and a function of sharing informationwith another portable game machine by wireless communication. Note thatfunctions of the portable game machine illustrated in FIG. 4C are notlimited to them, and the portable game machine can have variousfunctions.

FIG. 4D illustrates an example of a cellular phone. A cellular phone7400 is provided with a display portion 7402 incorporated in a housing7401, an operation button 7403, an external connection port 7404, aspeaker 7405, a microphone 7406, and the like. Note that the cellularphone 7400 is manufactured by using the light-emitting device of oneembodiment of the present invention for the display portion 7402.

When the display portion 7402 of the cellular phone 7400 illustrated inFIG. 4D is touched with a finger or the like, data can be input into thecellular phone. Furthermore, operations such as making a call andcreating e-mail can be performed by touching the display portion 7402with a finger or the like.

There are mainly three screen modes of the display portion 7402. Thefirst mode is a display mode mainly for displaying an image. The secondmode is an input mode mainly for inputting information such ascharacters. The third mode is a display-and-input mode in which twomodes of the display mode and the input mode are combined.

For example, in the case of making a call or creating e-mail, a textinput mode mainly for inputting text is selected for the display portion7402 so that text displayed on the screen can be input.

When a sensing device including a sensor such as a gyroscope sensor oran acceleration sensor for detecting inclination is provided inside thecellular phone 7400, display on the screen of the display portion 7402can be automatically changed in direction by determining the orientationof the cellular phone 7400 (whether the cellular phone 7400 is placedhorizontally or vertically for a landscape mode or a portrait mode).

The screen modes are changed by touch on the display portion 7402 oroperation with the operation button 7403 of the housing 7401. The screenmodes can be switched depending on the kind of images displayed on thedisplay portion 7402. For example, when a signal of an image displayedon the display portion is a signal of moving image data, the screen modeis switched to the display mode. When the signal is a signal of textdata, the screen mode is switched to the input mode.

Moreover, in the input mode, if a signal detected by an optical sensorin the display portion 7402 is detected and the input by touch on thedisplay portion 7402 is not performed for a certain period, the screenmode may be controlled so as to be changed from the input mode to thedisplay mode.

The display portion 7402 may function as an image sensor. For example,an image of a palm print, a fingerprint, or the like is taken by thedisplay portion 7402 while in touch with the palm or the finger, wherebypersonal authentication can be performed. Furthermore, when a backlightor a sensing light source which emits near-infrared light is provided inthe display portion, an image of a finger vein, a palm vein, or the likecan be taken.

FIG. 4E illustrates an example of a foldable tablet terminal (in an openstate). A tablet terminal 7500 includes a housing 7501 a, a housing 7501b, a display portion 7502 a, and a display portion 7502 b. The housing7501 a and the housing 7501 b are connected by a hinge 7503 and can beopened and closed using the hinge 7503 as an axis. The housing 7501 aincludes a power switch 7504, operation keys 7505, a speaker 7506, andthe like. Note that the tablet terminal 7500 is manufactured by usingthe light-emitting device of one embodiment of the present invention foreither the display portion 7502 a or the display portion 7502 b, orboth.

Part of the display portion 7502 a or the display portion 7502 b can beused as a touch panel region, where data can be input by touchingdisplayed operation keys. For example, a keyboard can be displayed onthe entire region of the display portion 7502 a so that the displayportion 7502 a is used as a touch panel, and the display portion 7502 bcan be used as a display screen.

An indoor lighting device 7601, a roll-type lighting device 7602, a desklamp 7603, and a planar lighting device 7604 illustrated in FIG. 5A areeach an example of a lighting device which includes the light-emittingdevice of one embodiment of the present invention. Since thelight-emitting device of one embodiment of the present invention canhave a larger area, it can be used as a large-area lighting device.Furthermore, since the light-emitting device is thin, the light-emittingdevice can be mounted on a wall.

A desk lamp illustrated in FIG. 5B includes a lighting portion 7701, asupport 7703, a support base 7705, and the like. The light-emittingdevice of one embodiment of the present invention is used for thelighting portion 7701. In one embodiment of the present invention, alighting device whose light-emitting portion has a curved surface or alighting device including a flexible lighting portion can be achieved.Such use of a flexible light-emitting device for a lighting deviceenables a place having a curved surface, such as the ceiling ordashboard of a motor vehicle, to be provided with the lighting device,as well as increases the degree of freedom in design of the lightingdevice.

This embodiment can be combined with any other embodiment asappropriate.

Example 1 Synthesis Example 1

This example describes a method for synthesizing2-{3-[3-(benzo[b]naphtho[1,2-d]furan-8-yl)phenyl]phenyl}dibenzo[f,h]quinoxaline(abbreviation: 2mBnfBPDBq) represented by Structural Formula (101). Thisexample also describes a method for synthesizing2-(benzo[b]naphtho[1,2-d]furan-8-yl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolanethat is an organic compound of one embodiment of the present inventionrepresented by Structural Formula (201).

Step 1: Synthesis of 3-Chloro-2-fluorobenzeneboronic Acid

A synthesis scheme of Step 1 is shown in (B-1).

In a 500 mL three-neck flask was put 16 g (72 mmol) of1-bromo-3-chloro-2-fluorobenzene, and the air in the flask was replacedwith nitrogen; then, 200 mL of tetrahydrofuran (THF) was added and thesolution was cooled down to −80° C. under a nitrogen stream. To thissolution, 48 mL (76 mmol) of n-butyl lithium (a 1.6 mol/L hexanesolution) was added dropwise with a syringe, and then the mixture wasstirred for 1.5 hours at the same temperature. After the stirring, 9.0mL (80 mmol) of trimethyl borate was added to this mixture. While thetemperature was raised to room temperature, the mixture was stirred forapproximately 19 hours. After the stirring, approximately 100 mL of a 1mol/L hydrochloric acid was added to the resulting solution and themixture was stirred. The organic layer of this mixture was washed withwater and the aqueous layer was subjected to extraction with toluenetwice. The solution of the extract and the organic layer were combinedand washed with saturated brine. The resulting organic layer was driedwith magnesium sulfate, and this mixture was gravity-filtered. Theresulting filtrate was concentrated to give 4.5 g of a pale yellow solidof a target substance, in a yield of 35%.

Step 2: Synthesis of 1-(3-Chloro-2-fluorophenyl)-2-naphthol

A synthesis scheme of Step 2 is shown in (B-2).

In a 200 mL three-neck flask were put 5.8 g (26 mmol) of1-bromo-2-naphthol, 4.5 g (26 mmol) of 3-chloro-2-fluorobenzeneboronicacid, and 0.40 g (1.3 mmol) of tri(ortho-tolyl)phosphine, and the air inthe flask was replaced with nitrogen. To this mixture, 150 mL oftoluene, 50 mL of ethanol, and 21 mL of an aqueous solution of potassiumcarbonate (2.0 mol/L) were added. The mixture was degassed by beingstirred while the pressure in the flask was reduced; then, the air inthe flask was replaced with nitrogen. To this mixture was added 58 mg(0.26 mmol) of palladium(II) acetate, and the resulting mixture wasstirred at 90° C. under a nitrogen stream for 7 hours. After thestirring, the organic layer of the mixture was washed with water and theaqueous layer was subjected to extraction with toluene. The solution ofthe extract combined with the organic layer was washed with saturatedbrine, and the organic layer was dried with magnesium sulfate. Theresulting mixture was gravity-filtered, and the resulting filtrate wasconcentrated to give a brown liquid. The liquid was purified by silicagel column chromatography using a mixed solvent (toluene: hexane=9:1) asa developing solvent, so that 3.1 g of a brown liquid of a targetsubstance was produced in a yield of 44%.

Step 3: Synthesis of 8-Chlorobenzo[b]naphtho[1,2-d]furan

A synthesis scheme of Step 3 is shown in (B-3).

In a 300 mL recovery flask were put 3.1 g (11 mmol) of1-(3-chloro-2-fluorophenyl)-2-naphthol, 70 mL of N-methyl-2-pyrrolidone,and 4.2 g (31 mmol) of potassium carbonate, and this mixture was stirredat 150° C. in the air for 7 hours. After the stirring, approximately 50mL of water and approximately 50 mL of hydrochloric acid (1.0 mol/L)were added to the resulting mixture. To the resulting solution was addedapproximately 100 mL of ethyl acetate; then, the aqueous layer wassubjected to extraction with ethyl acetate three times. The solution ofthe extract combined with the organic layer was washed with a saturatedaqueous solution of sodium hydrogen carbonate and saturated brine, andmagnesium sulfate was then added. The mixture was gravity-filtered, andthe resulting filtrate was concentrated to give 2.9 g of a pale brownsolid of a target substance in a yield of over 99%.

¹H NMR data of the pale brown solid are as follows:

¹H NMR (CDCl₃, 500 MHz): δ=7.42 (t, J=4.7 Hz, 1H), 7.51 (d, J=4.5 Hz,1H), 7.58 (t, J=4.5 Hz, 1H), 7.75 (t, J=4.5 Hz, 1H), 7.85 (d, J=5.4 Hz,1H), 7.98 (d, J=5.1 Hz, 1H), 8.05 (d, J=4.8 Hz, 1H), 8.30 (d, J=4.2 Hz,1H), 8.59 (d, J=4.8 Hz, 1H).

Step 4: Synthesis of2-(Benzo[b]naphtho[1,2-d]furan-8-yl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane

A synthesis scheme of Step 4 is shown in (B-4).

In a 200 mL three-neck flask were put 2.5 g (10 mmol) of8-chlorobenzo[b]naphtho[1,2-d]furan, 2.5 g (10 mmol) ofbis(pinacolato)diboron, and 2.9 g (30 mmol) of potassium acetate, andthe air in the flask was replaced with nitrogen. To this mixture, 50 mLof 1,4-dioxane was added. The mixture was degassed by being stirredwhile the pressure in the flask was reduced; then, the air in the flaskwas replaced with nitrogen. To this mixture were added 22 mg (0.10 mmol)of palladium(II) acetate and 71 mg (0.20 mmol) ofdi(1-adamantyl)-n-butylphosphine, and the mixture was refluxed for 18hours. After the reflux, the resulting mixture was suction-filtered, andthe resulting filtrate was concentrated to give 2.5 g of a brown solidof a target substance in a yield of 73%.

¹H NMR data of the brown solid are as follows:

¹H NMR (CDCl₃, 500 MHz): δ=1.26 (s, 12H), 7.48 (t, J=4.5 Hz, 1H), 7.54(dt, J=0.9 Hz, J=4.8 Hz, 1H), 7.71 (dt, J=0.9 Hz, J=4.8 Hz, 1H), 7.88(d, J=5.1 Hz, 1H), 7.93-7.91 (m, 2H), 8.02 (d, J=4.8 Hz, 1H), 8.51 (dd,J=0.9 Hz, J=4.8 Hz, 1H), 8.63 (d, J=8.6 Hz, 1H).

In addition, FIGS. 6A and 6B show ¹H NMR charts. Note that FIG. 6B is achart showing an enlarged part of FIG. 6A in the range of 7.00 ppm to9.00 ppm.

Step 5: Synthesis of 2mBnfBPDBq

A synthesis scheme of Step 5 is shown in (B-5).

In a 200 mL three-neck flask were put 1.5 g (3.2 mmol) of2-(3′-bromobiphenyl-3-yl)dibenzo[f,h]quinoxaline, 1.1 g (3.2 mmol) of2-(benzo[b]naphtho[1,2-d]furan-8-yl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane,and 3.2 g (10 mmol) of cesium carbonate, and the air in the flask wasreplaced with nitrogen. Then, 16 mL of toluene was added to thismixture. The mixture was degassed by being stirred while the pressure inthe flask was reduced; then, the air in the flask was replaced withnitrogen. After 34 mg (30 mol) oftetrakis(triphenylphosphine)palladium(0) was added to this mixture, themixture was stirred at 100° C. under a nitrogen stream for 10 hours. Tothe resulting mixture, approximately 100 mL of toluene was added; then,this mixture was refluxed, in which a solid was precipitated anddissolved. This mixture was suction-filtered. The resulting filtrate wasleft standing, whereby recrystallization occurred. Thus, 1.0 g of a paleyellow solid of a target substance was produced in a yield of 51%.

By a train sublimation method, 0.76 g of the pale yellow solid waspurified. The sublimation purification was conducted by heating of thepale yellow solid at 330° C. under a pressure of 3.2 Pa. As a result ofthe sublimation purification, 0.36 g of a pale yellow solid was providedat a collection rate of 51%.

This compound was identified as 2mBnfBPDBq, which was the targetsubstance, by nuclear magnetic resonance (NMR) spectroscopy.

¹H NMR data of the obtained substance are as follows:

¹H NMR (CDCl₃, 500 MHz): δ=7.58 (t, J=₂ 4.2 Hz, 1H), 7.62 (t, J=4.7 Hz,1H), 7.73-7.86 (m, 10H), 7.90 (d, J=4.8 Hz, 1H), 7.92 (d, J=5.1 Hz, 1H),8.04 (t, J=4.5 Hz, 2H), 8.32 (s, 1H), 8.36 (d, J=4.5 Hz, 1H), 8.45 (d,J=4.2 Hz, 1H), 8.66-8.71 (m, 4H), 9.26 (dd, J=4.5 Hz, J₂=1.2 Hz, 1H),9.45 (d, J=4.8 Hz, 1H), 9.49 (s, 1H).

In addition, FIGS. 7A and 7B show ¹H NMR charts. Note that FIG. 7B is achart showing an enlarged part of FIG. 7A in the range of 7.00 ppm to10.0 ppm.

Furthermore, FIG. 8A shows an absorption spectrum of a toluene solutionof 2mBnfBPDBq, and FIG. 8B shows an emission spectrum thereof. FIG. 9Ashows an absorption spectrum of a thin film of 2mBnfBPDBq and FIG. 9Bshows an emission spectrum thereof. The absorption spectrum was measuredusing an ultraviolet-visible spectrophotometer (V-550, produced by JASCOCorporation). The measurements were performed with samples prepared byputting the solution in a quartz cell and depositing the thin film ontoa quartz substrate by evaporation. The absorption spectrum of thesolution was obtained by subtracting the absorption spectra of thequartz cell and toluene from those of the quartz cell and the solution,and the absorption spectrum of the thin film was obtained by subtractingthe absorption spectrum of a quartz substrate from the absorptionspectra of the thin film on the quartz substrate. In FIGS. 8A and 8B andFIGS. 9A and 9B, the horizontal axis indicates wavelength (nm) and thevertical axis indicates intensity (arbitrary unit). In the case of thetoluene solution, absorption peaks are observed around 355 nm and 368nm, and emission wavelength peaks are observed at 386 nm and 406 nm(excitation wavelength: 330 nm). In the case of the thin film,absorption peaks are observed around 211 nm, 259 nm, 318 nm, 329 nm, 346nm, 369 nm, and 384 nm, and an emission wavelength peak is observed at437 nm (excitation wavelength: 347 nm).

Electrochemical characteristics of a 2mBnfBPDBq solution were alsomeasured.

As a measuring method, cyclic voltammetry (CV) measurement was employed.An electrochemical analyzer (ALS model 600A or 600C, produced by BASInc.) was used for the measurement.

For the measurement of the oxidation characteristics, the potential ofthe working electrode with respect to the reference electrode wasscanned from 0.00 V to 1.50 V and then from 1.50 V to 0.00 V. Anobserved oxidation peak had 76% of the initial intensity even after 100cycles. This indicates that 2mBnfBPDBq has properties effective againstrepetition of redox reactions between an oxidized state and a neutralstate. FIG. 10A shows the measurement results of the oxidationcharacteristics.

For the measurement of the reduction characteristics, the potential ofthe working electrode with respect to the reference electrode wasscanned from −1.05 V to −2.10 V and then from −2.10 V to −1.05 V. Anobserved reduction peak had 73% of the initial intensity even after 100cycles. This indicates that 2mBnfBPDBq has properties effective againstrepetition of redox reactions between a reduced state and a neutralstate. FIG. 10B shows the measurement results of the reductioncharacteristics.

As for a solution used for the CV measurement, dehydrateddimethylformamide (DMF, produced by Sigma-Aldrich Co. LLC., 99.8%,catalog No. 22705-6) was used as a solvent, and tetra-n-butylammoniumperchlorate (n-Bu₄NClO₄, produced by Tokyo Chemical Industry Co., Ltd.,catalog No. T0836), which was a supporting electrolyte, was dissolved inthe solvent such that the concentration of tetra-n-butylammoniumperchlorate was 100 mmol/L. Furthermore, the object to be measured wasdissolved in the solvent such that the concentration thereof was 2mmol/L. A platinum electrode (produced by BAS Inc., PTE platinumelectrode) was used as a working electrode, a platinum electrode(produced by BAS Inc., Pt counter electrode for VC-3 (5 cm)) was used asan auxiliary electrode, and an Ag/Ag⁺ electrode (produced by BAS Inc.,RE-7 reference electrode for nonaqueous solvent) was used as a referenceelectrode. Note that the measurement was conducted at room temperature(20° C. to 25° C.). In addition, the scan rate at the CV measurement wasset to 0.1 V/sec in all the measurement. Note that the potential energyof the reference electrode with respect to the vacuum level was assumedto be −4.94 [eV] in this example.

On the assumption that the intermediate potential (the half-wavepotential) between the oxidation peak potential E_(pa) and the reductionpeak potential E_(pc) which are obtained in the CV measurementcorresponds to the HOMO level, the HOMO level of 2mBnfBPDBq wascalculated to be −6.13 eV, and the LUMO level of 2mBnfBPDBq wascalculated to be −2.95 eV. Accordingly, the band gap (ΔE) of 2mBnfBPDBqwas found to be 3.08 eV.

Furthermore, 2mBnfBPDBq was subjected to thermogravimetry-differentialthermal analysis. The measurement was conducted by using a high vacuumdifferential type differential thermal balance (TG/DTA 2410SA, producedby Bruker AXS K.K.). The measurement was carried out under a nitrogenstream (flow rate: 200 mL/min) at normal pressure at a temperaturerising rate of 10° C./min. From relationship between weight andtemperature (thermogravimetry), the 5% weight loss temperature and themelting point of 2mBnfBPDBq were 468° C. and 292° C., respectively.Accordingly, it was shown that 2mBnfBPDBq has high heat resistance.

Furthermore, 2mBnfBPDBq was subjected to mass spectrometric (MS)analysis by liquid chromatography mass spectrometry (LC-MS).

In the analysis by LC-MS, liquid chromatography (LC) separation wascarried out with UltiMate 3000 manufactured by Thermo Fisher ScientificK.K., and mass spectrometric (MS) analysis was carried out with QExactive manufactured by Thermo Fisher Scientific K.K. ACQUITY UPLC BEHC8 (2.1×100 mm, 1.7 μm) was used as a column for the LC separation, andthe column temperature was 40° C. Acetonitrile was used for Mobile PhaseA and a 0.1% aqueous solution of formic acid was used for Mobile PhaseB. Analysis was performed by a gradient method for 5 minutes, in whichthe proportion of acetonitrile was 80% at the start of the analysis andincreased linearly to reach 95% after 5 minutes from the start of theanalysis. A sample was prepared in such a manner that 2mBnfBPDBq wasdissolved in dimethylformamide at a given concentration and the mixturewas diluted with acetonitrile. The injection amount was 10.0 μL.

In the MS analysis, ionization was carried out by an electrosprayionization (ESI) method, and measurement was carried out bytargeted-MS². Conditions of an ion source were set as follows: the flowrates of a sheath gas, an Aux gas, and a Sweep gas were 50, 10, and 0,respectively, the spray voltage was 3.5 kV, the capillary temperaturewas 350° C., the S lens voltage was 55.0, and the HESI heatertemperature was 350° C. The resolution was 70000, the AGC target was3e6, the mass range was m/z=83.00 to 1245.00, and the detection wasperformed in a positive mode.

A component with m/z of 599.21±10 ppm that underwent the ionizationunder the above-described conditions was collided with an argon gas in acollision cell to dissociate into product ions, and MS/MS measurementwas carried out. Ions which were generated under a normalized collisionenergy (NCE) for the collision with argon of 55 were detected with aFourier transform mass spectrometer (FT MS). FIGS. 11A and 11B show themeasurement results.

The results in FIGS. 11A and 11B demonstrate that product ions of2mBnfBPDBq are detected around m/z=229 and m/z=220. Note that theresults in FIGS. 11A and 11B show characteristics derived from2mBnfBPDBq and thus can be regarded as important data for identifying2mBnfBPDBq contained in a mixture.

The product ion around m/z=229 is presumed to be a cation derived fromdibenzo[f,h]quinoxaline in 2mBnfBPDBq, and indicates a partial structureof the heterocyclic compound of one embodiment of the present invention.The product ion around m/z=220 is presumed to be a cation that wasderived from an alcohol formed by cleavage of an ether linkage inbenzo[b]naphtho[1,2-d]furan (Structural Formula (10) or StructuralFormula (11)), and indicates a partial structure of the heterocycliccompound of one embodiment of the present invention.

The product ion around m/z=572 is presumed to be a cation derived from2mBnfBPDBq in the state where one CH and one N are dissociated fromdibenzo[f,h]quinoxaline in 2mBnfBPDBq, and indicates a partial structureof the heterocyclic compound of one embodiment of the present invention.In particular, this is one of features of the heterocyclic compound ofone embodiment of the present invention in which a substituent (in2mBnfBPDBq, a biphenyl skeleton bonded to a benzo[b]naphtho[1,2-d]furanskeleton) is bonded to the 2-position of dibenzo[f,h]quinoxaline.

Calculation and measurement were performed to find out the T₁ level of2mBnfBPDBq.

The calculating method is described below. Note that Gaussian 09 wasused as the quantum chemistry computational program. A high performancecomputer (Altix 4700, manufactured by SGI Japan, Ltd.) was used for thecalculations.

First, the most stable structure in the singlet ground state wascalculated using the density functional theory. As a basis function,6-311G (a basis function of a triple-split valence basis set using threecontraction functions for each valence orbital) was applied to all theatoms. By the above basis function, for example, is to 3 s orbitals areconsidered in the case of hydrogen atoms, while is to 4 s and 2p to 4porbitals are considered in the case of carbon atoms. Furthermore, toimprove calculation accuracy, the p function and the d function aspolarization basis sets were added respectively to hydrogen atoms andatoms other than hydrogen atoms. As a functional, B3LYP was used.

Next, the most stable structure in the lowest excited triplet state wascalculated. Then, vibration analysis was conducted on the most stablestructures in the singlet ground state and in the lowest excited tripletstate, and a zero-point corrected energy difference was obtained. The T₁level was calculated from the zero-point corrected energy difference. Asa basis function, 6-311G (d, p) was used. As a functional, B3LYP wasused.

From the above calculation, the T₁ level of 2mBnfBPDBq was estimated tobe 2.41 eV.

Phosphorescence of 2mBnfBPDBq was measured to support the quantumchemical calculation.

An evaporated film of 2mBnfBPDBq was formed and was subjected to alow-temperature photoluminescence (PL) method, and the T₁ level thereofwas estimated from the measured phosphorescence spectrum. Note that theT₁ level was estimated from a peak wavelength on the shortest wavelengthside of the phosphorescence spectrum. The measurement was performed byusing a PL microscope, LabRAM HR-PL, produced by HORIBA, Ltd., a He—Cdlaser (325 nm) as excitation light, and a CCD detector at a measurementtemperature of 10 K.

For the measurement, a thin film was formed over a quartz substrate to athickness of 50 nm and another quartz substrate was attached to thedeposition surface in a nitrogen atmosphere.

The measurement results show that 2mBnfBPDBq has a T₁ level of 2.40 eV.The results indicate that the values of the T₁ levels measured in thisexample are close to the values of the T₁ levels calculated by thequantum chemical calculation. Therefore, the values of the T₁ levelsobtained in this example are citable as parameters for forming thelight-emitting element of one embodiment of the present invention.

Example 1 revealed that the heterocyclic compound of one embodiment ofthe present invention represented by General Formula (G1) has a high T₁level. Accordingly, the use of the heterocyclic compound of oneembodiment of the present invention makes it possible to provide alight-emitting element with high efficiency.

Example 2

In this example, a T₁ level was calculated to provide evidence that theheterocyclic compound of one embodiment of the present invention has ahigh T₁ level.

The calculation method described in Example 1 was used.

In this example, the T₁ levels of five kinds of partial structuresrepresented by chemical formulae below were calculated. As the partialstructures, 8PBnf, 9PBnf, 10PBnf, and 11PBnf, and 6PBnf that is acomparative example were used. Each of 8PBnf, 9PBnf, 10PBnf, and 11PBnfhas a structure in which a phenyl group is bonded to any one of the 8-to 11-positions of benzo[b]naphtho[1,2-d]furan (an example of astructure in which a phenyl group is bonded to the benzene ring).Meanwhile, 6PBnf has a structure in which a phenyl group is bonded tothe 6-position of benzo[b]naphtho[1,2-d]furan (an example of a structurein which a phenyl group is bonded to the naphthalene ring).

The calculation results are shown in Table 1.

TABLE 1 Partial structure 8PBnf 9PBnf 10PBnf 11PBnf 6PBnf T₁ level (eV)2.41 2.35 2.41 2.38 2.29

The results revealed that 8PBnf, 9PBnf, 10PBnf, and 11PBnf, in which thephenyl group is bonded to the benzene ring ofbenzo[b]naphtho[1,2-d]furan, each have a high T₁ level. Furthermore,8PBnf, 9PBnf, 10PBnf, and 11PBnf were each found to have a higher T₁level than 6PBnf as the comparative example, in which a phenyl group isbonded to the naphthalene ring of benzo[b]naphtho[1,2-d]furan. The aboveshows that the heterocyclic compound of one embodiment of the presentinvention has a high T₁ level and that the use of the heterocycliccompound makes it possible to provide a light-emitting element with highefficiency.

Example 3

In this example, the light-emitting element of one embodiment of thepresent invention will be described with reference to FIG. 12. Chemicalformulae of materials used in this example are shown below. Note thatthe chemical formulae of the materials which are shown above areomitted.

A method for fabricating a light-emitting element 1 of this example willbe described below.

(Light-Emitting Element 1)

A film of indium tin oxide containing silicon (ITSO) was formed over aglass substrate 1100 by a sputtering method, so that a first electrode1101 which functions as an anode was formed. The thickness thereof was110 nm and the electrode area was 2 mm×2 mm.

Next, as pretreatment for forming the light-emitting element over theglass substrate 1100, UV-ozone treatment was performed for 370 secondsafter washing of a surface of the glass substrate 1100 with water andbaking that was performed at 200° C. for 1 hour.

After that, the glass substrate 1100 was transferred into a vacuumevaporation apparatus where the pressure had been reduced toapproximately 10⁻⁴ Pa, and was subjected to vacuum baking at 170° C. for30 minutes in a heating chamber of the vacuum evaporation apparatus, andthen the glass substrate 1100 was cooled down for approximately 30minutes.

Then, the glass substrate 1100 over which the first electrode 1101 wasformed was fixed to a substrate holder provided in the vacuumevaporation apparatus so that the surface on which the first electrode1101 was formed faced downward. The pressure in the vacuum evaporationapparatus was reduced to approximately 10⁻⁴ Pa. After that, over thefirst electrode 1101, 4,4′,4″-(1,3,5-benzenetriyl)tri(dibenzothiophene)(abbreviation: DBT3P-II) and molybdenum(VI) oxide were deposited byco-evaporation, so that a hole-injection layer 1111 was formed. Thethickness of the hole-injection layer 1111 was set to 20 nm, and theweight ratio of DBT3P-II to molybdenum oxide was adjusted to 4:2(=DBT3P-II: molybdenum oxide). Note that the co-evaporation methodrefers to an evaporation method in which evaporation is carried out froma plurality of evaporation sources at the same time in one treatmentchamber.

Next, a film of 4-phenyl-4′-(9-phenylfluoren-9-yl)triphenylamine(abbreviation: BPAFLP) was formed to a thickness of 20 nm over thehole-injection layer 1111 to form a hole-transport layer 1112.

Furthermore, a light-emitting layer 1113 was formed over thehole-transport layer 1112 by co-evaporation of 2mBnfBPDBq,N-(1,1′-biphenyl-4-yl)-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-9,9-dimethyl-9H-fluoren-2-amine (abbreviation: PCBBiF), and(acetylacetonato)bis(4,6-diphenylpyrimidinato)iridium(III)(abbreviation: [Ir(dppm)₂(acac)]). Here, a 20-nm-thick layer which wasformed with the weight ratio of 2mBnIBPDBq to PCBBiF and[Ir(dppm)₂(acac)] adjusted to 0.7:0.3:0.05 (=2mBnfBPDBq: PCBBiF:[Ir(dppm)₂(acac)]) and a 20-nm-thick layer which was formed with theweight ratio adjusted to 0.8:0.2:0.05 (=2mBnfBPDBq: PCBBiF:[Ir(dppm)₂(acac)]) were stacked.

Next, a film of 2mBnfBPDBq was formed to a thickness of 20 nm over thelight-emitting layer 1113 and then a film of bathophenanthroline(abbreviation: BPhen) was formed to a thickness of 10 nm, so that anelectron-transport layer 1114 was formed.

After that, over the electron-transport layer 1114, a film of lithiumfluoride (LiF) was formed by evaporation to a thickness of 1 nm to forman electron-injection layer 1115.

Lastly, aluminum was deposited by evaporation to a thickness of 200 nmto form a second electrode 1103 functioning as a cathode. Thus, thelight-emitting element 1 of this example was fabricated.

Note that in all the above evaporation steps, evaporation was performedby a resistance-heating method.

Table 2 shows the element structure of the light-emitting elementfabricated as described above in this example.

TABLE 2 Hole- Hole- Electron- First injection transport injection Secondelectrode layer layer Light-emitting layer Electron-transport layerlayer electrode Light- ITSO DBT3P-II:MoO_(x) BPAFLP2mBnfBPDBq:PCBBiF:[Ir(dppm)₂(acac)] 2mBnfBPDBq BPhen LiF Al emitting 110nm (=4:2) 20 nm (=0.7:0.3:0.05) (=0.8:0.2:0.05) 20 nm 10 nm 1 nm 200 nmelement 1 20 nm 20 nm 20 nm

The light-emitting element of this example was sealed in a glove boxunder a nitrogen atmosphere so as not to be exposed to the air. Then,the operation characteristics of the light-emitting element weremeasured. Note that the measurement was carried out at room temperature(in an atmosphere kept at 25° C.).

FIG. 13 shows luminance-current density characteristics of thelight-emitting element 1. In FIG. 13, the horizontal axis indicatescurrent density (mA/cm²), and the vertical axis indicates luminance(cd/m²). FIG. 14 shows luminance-voltage characteristics. In FIG. 14,the horizontal axis indicates voltage (V) and the vertical axisindicates luminance (cd/m²). FIG. 15 shows current efficiency-luminancecharacteristics. In FIG. 15, the horizontal axis indicates luminance(cd/m²) and the vertical axis indicates current efficiency (cd/A). FIG.16 shows current-voltage characteristics. In FIG. 16, the horizontalaxis indicates voltage (V) and the vertical axis indicates current (mA).FIG. 17 shows external quantum efficiency-luminance characteristics. InFIG. 17, the horizontal axis indicates luminance (cd/m²) and thevertical axis indicates external quantum efficiency (%). Table 3 showsthe voltage (V), current density (mA/cm²), CIE chromaticity coordinates(x, y), current efficiency (cd/A), power efficiency (lm/W), and externalquantum efficiency (%) of the light-emitting element 1 at a luminance of1000 cd/m².

TABLE 3 External Current Current Power quantum Voltage density Luminanceefficiency efficiency efficiency (V) (mA/cm²) Chromaticity xChromaticity y (cd/m²) (cd/A) (lm/W) (%) Light- 3.0 1.3 0.55 0.44 100082 86 29 emitting element 1

The CIE chromaticity coordinates (x, y) at a luminance of 1000 cd/m² ofthe light-emitting element 1 were (0.55, 0.44) and the light-emittingelement 1 exhibited orange light emission. These results show thatorange light emission originating from [Ir(dppm)₂(acac)] was providedfrom the light-emitting element 1.

The measurement results of the operation characteristics show that thelight-emitting element 1 has high emission efficiency and a low drivevoltage.

A reliability test of the light-emitting element 1 was conducted. FIG.18 shows results of the reliability test. In FIG. 18, the vertical axisindicates normalized luminance (%) with an initial luminance of 100% andthe horizontal axis indicates driving time (h) of the element. In thereliability test, which was conducted at room temperature, thelight-emitting element 1 was driven under the conditions where theinitial luminance was set to 5000 cd/m² and the current density wasconstant. FIG. 18 shows that the light-emitting element 1 kept 90% ofthe initial luminance after 2820 hours. The results of the reliabilitytest show that the light-emitting element 1 has a long lifetime.

Example 4

In this example, the light-emitting element of one embodiment of thepresent invention will be described with reference to FIG. 12. Chemicalformulae of materials used in this example are shown below. Note thatthe chemical formulae of the materials which are shown above areomitted.

A method for fabricating a light-emitting element 2 of this example willbe described below.

(Light-Emitting Element 2)

In the light-emitting element 2, components other than thelight-emitting layer 1113 and the electron-transport layer 1114 wereformed in a similar manner to the light-emitting element 1. Here, onlydifferent steps from the method for fabricating the light-emittingelement 1 are described.

The light-emitting layer 1113 of the light-emitting element 2 was formedby co-depositing 2mBnfBPDBq, PCBBiF, and(acetylacetonato)bis(6-tert-butyl-4-phenylpyrimidinato)iridium(III)(abbreviation: [Ir(tBuppm)₂(acac)]) by evaporation. Here, a 20-nm-thicklayer which was formed with the weight ratio of 2mBnfBPDBq to PCBBiF and[Ir(tBuppm)₂(acac)] adjusted to 0.7:0.3:0.05 (=2mBnfBPDBq: PCBBiF:[Ir(tBuppm)₂(acac)]) and a 20-nm-thick layer which was formed with theweight ratio adjusted to 0.8:0.2:0.05 (=2mBnfBPDBq: PCBBiF:[Ir(tBuppm)₂(acac)]) were stacked.

The electron-transport layer 1114 of the light-emitting element 2 wasformed by depositing 2mBnfBPDBq to a thickness of 15 nm and furtherdepositing BPhen to a thickness of 10 nm.

Table 4 shows the element structure of the light-emitting elementfabricated as described above in this example.

TABLE 4 Hole- Hole- Electron- First injection transport injection Secondelectrode layer layer Light-emitting layer Electron-transport layerlayer electrode Light- ITSO DBT3P-II:MoO_(x) BPAFLP2mBnfBPDBq:PCBBiF:[Ir(tBuppm)₂(acac)] 2mBnfBPDBq BPhen LiF Al emitting110 nm (=4:2) 20 nm (=0.7:0.3:0.05) (=0.8:0.2:0.05) 15 nm 10 nm 1 nm 200nm element 2 20 nm 20 nm 20 nm

The light-emitting element of this example was sealed in a glove boxunder a nitrogen atmosphere so as not to be exposed to the air. Then,the operation characteristics of the light-emitting element weremeasured. Note that the measurement was carried out at room temperature(in an atmosphere kept at 25° C.).

FIG. 19 shows luminance-current density characteristics of thelight-emitting element 2. In FIG. 19, the horizontal axis indicatescurrent density (mA/cm²), and the vertical axis indicates luminance(cd/m²). FIG. 20 shows luminance-voltage characteristics. In FIG. 20,the horizontal axis indicates voltage (V) and the vertical axisindicates luminance (cd/m²). FIG. 21 shows current efficiency-luminancecharacteristics. In FIG. 21, the horizontal axis indicates luminance(cd/m²) and the vertical axis indicates current efficiency (cd/A). FIG.22 shows current-voltage characteristics. In FIG. 22, the horizontalaxis indicates voltage (V) and the vertical axis indicates current (mA).FIG. 23 shows external quantum efficiency-luminance characteristics. InFIG. 23, the horizontal axis indicates luminance (cd/m²) and thevertical axis indicates external quantum efficiency (%). Table 5 showsthe voltage (V), current density (mA/cm²), CIE chromaticity coordinates(x, y), current efficiency (cd/A), power efficiency (lm/W), and externalquantum efficiency (%) of the light-emitting element 2 at a luminance of700 cd/m².

TABLE 5 External Current Current Power quantum Voltage density Luminanceefficiency efficiency efficiency (V) (mA/cm²) Chromaticity xChromaticity y (cd/m²) (cd/A) (lm/W) (%) Light- 2.7 0.72 0.40 0.59 70097 113 25 emitting element 2

The CIE chromaticity coordinates (x, y) at a luminance of 700 cd/m² ofthe light-emitting element 2 were (0.40, 0.59) and the light-emittingelement 2 exhibited yellow green light emission. These results show thatyellow green light emission originating from [Ir(tBuppm)₂(acac)] wasprovided from the light-emitting element 2.

The measurement results of the operation characteristics show that thelight-emitting element 2 has high emission efficiency and a low drivevoltage.

A reliability test of the light-emitting element 2 was conducted. FIG.24 shows results of the reliability test. In FIG. 24, the vertical axisindicates normalized luminance (%) with an initial luminance of 100% andthe horizontal axis indicates driving time (h) of the element. In thereliability test, which was conducted at room temperature, thelight-emitting element 2 was driven under the conditions where theinitial luminance was set to 5000 cd/m² and the current density wasconstant. FIG. 24 shows that the light-emitting element 2 kept 86% ofthe initial luminance after 810 hours. The results of the reliabilitytest show that the light-emitting element 2 has a long lifetime.

Example 5 Synthesis Example 2

This example describes a method for synthesizing2-[3′-(6-phenylbenzo[b]naphtho[1,2-d]furan-8-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline(abbreviation: 2mBnfBPDBq-02) represented by Structural Formula (140).

Step 1-1: Synthesis of 6-Iodobenzo[b]naphtho[1,2-d]furan

A synthesis scheme of Step 1-1 is shown in (C-1).

Into a 500 mL three-neck flask was put 8.5 g (39 mmol) ofbenzo[b]naphtho[1,2-d]furan, and the air in the flask was replaced withnitrogen. Then, 195 mL of tetrahydrofuran (THF) was added thereto. Thissolution was cooled to −75° C. Then, 25 mL (40 mmol) of n-butyllithium(a 1.59 mol/L n-hexane solution) was dropped into this solution. Afterthe drop, the resulting solution was stirred at room temperature for 1hour. After the stirring, the resulting solution was cooled to −75° C.Into this solution, a solution in which 10 g (40 mmol) of iodine wasdissolved in 40 mL of THF was dropped. After the drop, the resultingsolution was stirred for 17 hours while the temperature of the solutionwas returned to room temperature. After the stirring, an aqueoussolution of sodium thiosulfate was added to the mixture, and theresulting mixture was stirred for 1 hour. Then, the organic layer of themixture was washed with water and dried with magnesium sulfate. Afterthe drying, the mixture was gravity-filtered to give a solution. Theresulting solution was suction-filtered through Celite (Catalog No.531-16855 produced by Wako Pure Chemical Industries, Ltd., the sameapplies to Celite described below and a repetitive description thereofis omitted) and Florisil (Catalog No. 540-00135 produced by Wako PureChemical Industries, Ltd., the same applies to Florisil described belowand a repetitive description thereof is omitted) to give a filtrate. Theresulting filtrate was concentrated to give a solid. The resulting solidwas recrystallized from toluene to give 6.0 g (18 mmol) of white powderof the target substance in a yield of 45%.

Step 1-2: Synthesis of 6-Phenylbenzo[b]naphtho[1,2-d]furan

A synthesis scheme of Step 1-2 is shown in (C-2).

Into a 200 mL three-neck flask were put 6.0 g (18 mmol) of6-iodobenzo[b]naphtho[1,2-d]furan, 2.4 g (19 mmol) of phenylboronicacid, 70 mL of toluene, 20 mL of ethanol, and 22 mL of an aqueoussolution of potassium carbonate (2.0 mol/L). This mixture was degassedby being stirred while the pressure was reduced. After the degassing,the air in the flask was replaced with nitrogen, and then 480 mg (0.42mmol) of tetrakis(triphenylphosphine)palladium(0) was added to themixture. The resulting mixture was stirred at 90° C. under a nitrogenstream for 12 hours. After the stirring, water was added to the mixture,and the aqueous layer was subjected to extraction with toluene. Thesolution of the extract combined with the organic layer was washed withwater and then dried with magnesium sulfate. The mixture wasgravity-filtered to give a filtrate. The resulting filtrate wasconcentrated to give a solid, and the resulting solid was dissolved intoluene. The resulting solution was suction-filtered through Celite,Florisil, and alumina to give a filtrate. The resulting filtrate wasconcentrated to give a solid. The resulting solid was recrystallizedfrom toluene to give 4.9 g (17 mmol) of a white solid of the targetsubstance in a yield of 93%.

Step 1-3: Synthesis of 8-Iodo-6-phenylbenzo[b]naphtho[1,2,d]furan

A synthesis scheme of Step 1-3 is shown in (C-3).

Into a 300 mL three-neck flask was put 4.9 g (17 mmnol) of6-phenylbenzo[b]naphtho[1,2-d]furan, and the air in the flask wasreplaced with nitrogen. Then, 87 mL of THF was added thereto. Theresulting solution was cooled to −75° C. Then, 11 mL (18 mmol) ofn-butyllithium (a 1.59 mol/L n-hexane solution) was dropped into thesolution. After the drop, the resulting solution was stirred at roomtemperature for 1 hour. After the stirring, the resulting solution wascooled to −75° C. Then, a solution in which 4.6 g (18 mmol) of iodinewas dissolved in 18 mL of THF was dropped into the resulting solution.The resulting solution was stirred for 17 hours while the temperature ofthe solution was returned to room temperature. After the stirring, anaqueous solution of sodium thiosulfate was added to the mixture, and theresulting mixture was stirred for 1 hour. Then, the organic layer of themixture was washed with water and dried with magnesium sulfate. Themixture was gravity-filtered to give a filtrate. The resulting filtratewas suction-filtered through Celite, Florisil, and alumina to give afiltrate. The resulting filtrate was concentrated to give a solid. Theresulting solid was recrystallized from toluene to give 3.7 g (8.8 mmol)of a target white solid in a yield of 53%.

Step 2: Synthesis of2-[3′-(Dibenzo[f,h]quinoxalin-2-yl)-biphenyl-3-yl]-4,4,5,5-tetramethyl-1,3,2-dioxaborolane

A synthesis scheme of Step 2 is shown in (C-4).

Into a 200 mL three-neck flask were put 1.8 g (3.9 mmol) of2-(3′-bromobiphenyl-3-yl)dibenzo[f,h]quinoxaline, 994 mg (3.9 mmol) ofbis(pinacolato)diboron, and 795 mg (8.0 mmol) of potassium acetate, andthe air in the flask was replaced with nitrogen. To this mixture, 20 mLof 1,4-dioxane was added, and the obtained mixture was degassed by beingstirred under reduced pressure; then, the air in the flask was replacedwith a nitrogen stream. The obtained mixture was stirred at 60° C., andto this mixture, 87 mg (0.1 mmol) of[1,1′-bis(diphenylphosphino)ferrocene]palladium(II) dichloridedichloromethane adduct was added. This mixture was stirred at 80° C. for9 hours. The reaction mixture was developed by silica gel thin layerchromatography (developing solvent: a mixed solvent of hexane:ethylacetate=10:1), so that a spot of the objective substance was observed.

Step 3: Synthesis of 2mBnfBPDBq-02

A synthesis scheme of Step 3 is shown in (C-5).

After the reaction by Step 2, the reaction by Step 3 was carried out inthe same container without work-up (posttreatment). To the mixtureobtained in Step 2, 1.6 g (3.9 mmol) of8-iodo-6-phenylbenzo[b]naphtho[1,2-d]furan obtained in Step 1-3, 60 mg(0.30 mmol) of palladium(II) acetate, and 2.2 g (6.6 mmol) of cesiumcarbonate were added, and this mixture was stirred at 100° C. for 6hours. After 20 mL of xylene was added to this mixture, stirring wasperformed at 120° C. for 9 hours. After the stirring, a precipitatedsolid was collected by suction filtration and washed with water andethanol in this order, and a resulting solid was dried; thus, 1.7 g of atarget brown solid was produced in a yield of 65%.

By a train sublimation method, 1.5 g of the obtained solid was purified.The sublimation purification was conducted under the conditions wherethe pressure was 3.2 Pa, the flow rate of an argon gas was 15 mL/min,and the solid was heated at 350° C. for 17 hours. After the heating,0.95 g of a pale brown solid was obtained at a collection rate of 63%.

Then, 0.95 g of the solid obtained by the sublimation purification waspurified by a train sublimation method. The sublimation purification wasconducted under the conditions where the pressure was 3.5 Pa, the flowrate of an argon gas was 15 mL/min, and the solid was heated at 350° C.for 17 hours. After the heating, 0.72 g of a pale brown solid wasobtained at a collection rate of 77%.

This compound was identified as 2mBnfBPDBq-02, which was the targetsubstance, by nuclear magnetic resonance (NMR) spectroscopy.

¹H NMR data of the obtained substance are as follows:

¹H NMR (tetrachloroethane-d₂, 500 MHz): δ=7.28-7.29 (m, 3H), 7.62 (t,J=7.5 Hz, 1H), 7.65-7.73 (m, 4H), 7.77-7.86 (m, 7H), 7.98-8.00 (m, 2H),8.03 (d, 1H), 8.07 (s, 1H), 8.10 (d, 1H), 8.38 (d, J=8.0 Hz, 1H),8.49-8.51 (m, 2H), 8.65-8.66 (m, 3H), 8.72 (d, J=8.5 Hz, 1H), 9.27 (d,J=7.0 Hz, 1H), 9.40 (d, J=8.0 Hz, 1H), 9.44 (s, 1H).

In addition, FIGS. 25A and 25B show ¹H NMR charts. Note that FIG. 25B isa chart showing an enlarged part of FIG. 25A in the range of 7.00 ppm to10.0 ppm.

Furthermore, FIG. 26A shows an absorption spectrum of a toluene solutionof 2mBnfBPDBq-02, and FIG. 26B shows an emission spectrum thereof. FIG.27A shows an absorption spectrum of a thin film of 2mBnfBPDBq-02 andFIG. 27B shows an emission spectrum thereof. For the measurement methodand measurement conditions of the absorption spectra, refer to thedescription in Example 1. In FIGS. 26A and 26B and FIGS. 27A and 27B,the horizontal axis indicates wavelength (nm) and the vertical axisindicates intensity (arbitrary unit). In the case of the toluenesolution, absorption peaks are observed around 322 nm, 353 nm, and 375nm, and emission wavelength peaks are observed at 385 nm and 405 nm(excitation wavelength: 330 nm). In the case of the thin film,absorption peaks are observed around 262 nm, 328 nm, 345 nm, 366 nm, and383 nm, and an emission wavelength peak is observed at 439 nm(excitation wavelength: 380 nm).

Electrochemical characteristics of a 2mBnfBPDBq-02 solution were alsomeasured.

For the measurement method, measurement conditions, and the like, referto the description in Example 1.

For the measurement of the oxidation characteristics, the potential ofthe working electrode with respect to the reference electrode wasscanned from 0.30 V to 1.30 V and then from 1.30 V to 0.30 V. Anobserved oxidation peak had 59% of the initial intensity even after 100cycles. This indicates that 2mBnfBPDBq-02 has properties effectiveagainst repetition of redox reactions between an oxidized state and aneutral state. FIG. 28A shows the measurement results of the oxidationcharacteristics.

For the measurement of the reduction characteristics, the potential ofthe working electrode with respect to the reference electrode wasscanned from −1.30 V to −2.10 V and then from −2.10 V to −1.30 V. Anobserved reduction peak had 78% of the initial intensity even after 100cycles. This indicates that 2mBnfBPDBq-02 has properties effectiveagainst repetition of redox reactions between a reduced state and aneutral state. FIG. 28B shows the measurement results of the reductioncharacteristics.

On the assumption that the intermediate potential (the half-wavepotential) between the oxidation peak potential E_(pa) and the reductionpeak potential E_(pc) which are obtained in the CV measurementcorresponds to the HOMO level, the HOMO level of 2mBnfBPDBq-02 wascalculated to be −6.06 eV, and the LUMO level of 2mBnfBPDBq-02 wascalculated to be −2.94 eV. Accordingly, the band gap (ΔE) of2mBnfBPDBq-02 was found to be 3.12 eV.

Furthermore, 2mBnfBPDBq-02 was subjected tothermogravimetry-differential thermal analysis. For the measurementmethod, measurement conditions, and the like, refer to the descriptionin Example 1. Measurement results show that the 5% weight losstemperature of 2mBnfBPDBq-02 was 500° C. or higher and the melting pointthereof was 273° C. Accordingly, it was shown that 2mBnfBPDBq-02 hashigh heat resistance.

Furthermore, 2mBnfBPDBq-02 was subjected to MS analysis by LC-MS.

Description of analysis conditions similar to those in Example 1 isomitted. In the analysis by LC-MS in this example, acetonitrile was usedfor Mobile Phase A and a 0.1% aqueous solution of formic acid was usedfor Mobile Phase B. Analysis was performed by a gradient method for 10minutes, in which the proportion of acetonitrile was 75% at the start ofthe analysis, kept at the value for 1 minute, and then increasedlinearly to reach 95% after 10 minutes from the start of the analysis.

In the MS analysis in this example, the resolution was 35000, the AGCtarget was 2e5, the mass range was m/z=50.00 to 705.00, and thedetection was performed in a positive mode.

A component with m/z of 674.24±10 ppm that underwent the ionizationunder the above-described conditions was collided with an argon gas in acollision cell to dissociate into product ions, and MS/MS measurementwas carried out. Ions which were generated under an NCE for thecollision with argon of 50 were detected with a Fourier transform massspectrometer (FT MS). FIGS. 35A and 35B show the results.

The results in FIGS. 35A and 35B demonstrate that product ions of2mBnfBPDBq-02 are detected around m/z=229 and m/z=220. Note that theresults in FIGS. 35A and 35B show characteristics derived from2mBnfBPDBq-02 and thus can be regarded as important data for identifying2mBnfBPDBq-02 contained in a mixture.

The product ion around m/z=229 is presumed to be a cation derived fromdibenzo[f,h]quinoxaline in 2mBnfBPDBq-02, and indicates a partialstructure of the heterocyclic compound of one embodiment of the presentinvention. The product ion around m/z=220 is presumed to be a cationthat was derived from an alcohol formed by cleavage of an ether linkagein benzo[b]naphtho[1,2-d]furan (Structural Formula (10) or StructuralFormula (11) in Example 1), and indicates a partial structure of theheterocyclic compound of one embodiment of the present invention.

Phosphorescence of 2mBnfBPDBq-02 was measured.

In this example, an evaporated film of 2mBnfBPDBq-02 was formed and wassubjected to a low-temperature PL method, and the T₁ level thereof wasestimated from the measured phosphorescence spectrum. Note that the T₁level was estimated from a peak wavelength on the shortest wavelengthside of the phosphorescence spectrum. The measurement was performed byusing a PL microscope, LabRAM HR-PL, produced by HORIBA, Ltd., a He—Cdlaser (325 nm) as excitation light, and a CCD detector at a measurementtemperature of 10 K.

For the measurement, a thin film was formed over a quartz substrate to athickness of 50 nm and another quartz substrate was attached to thedeposition surface in a nitrogen atmosphere.

According to the measurement results, a peak wavelength on the shortestwavelength side of the phosphorescence spectrum was 545 nm. Thus, the T₁level of 2mBnfBPDBq-02 was calculated to be 2.28 eV.

Example 6

In this example, the light-emitting element of one embodiment of thepresent invention will be described with reference to FIG. 12.

A method for fabricating a light-emitting element 3 of this example willbe described below.

(Light-Emitting Element 3)

In the light-emitting element 3, components other than thelight-emitting layer 1113 and the electron-transport layer 1114 wereformed in a similar manner to the light-emitting element 1. Here, onlydifferent steps from the method for fabricating the light-emittingelement 1 are described.

The light-emitting layer 1113 of the light-emitting element 3 was formedby co-depositing 2mBnfBPDBq-02, PCBBiF, and [Ir(dppm)₂(acac)] byevaporation. Here, a 20-nm-thick layer which was formed with the weightratio of 2mBnfBPDBq-02 to PCBBiF and [Ir(dppm)₂(acac)] adjusted to0.7:0.3:0.05 (=2mBnfBPDBq-02: PCBBiF: [Ir(dppm)₂(acac)]) and a20-nm-thick layer which was formed with the weight ratio adjusted to0.8:0.2:0.05 (=2mBnfBPDBq-02: PCBBiF: [Ir(dppm)₂(acac)]) were stacked.

The electron-transport layer 1114 of the light-emitting element 3 wasformed by depositing 2mBnfBPDBq-02 to a thickness of 20 nm and furtherdepositing BPhen to a thickness of 10 nm.

Table 6 shows the element structure of the light-emitting elementfabricated as described above in this example.

TABLE 6 First Hole- Hole- Electron- elec- injection transportElectron-transport injection Second trode layer layer Light-emitinglayer layer layer electrode Light- ITSO DBT3P-II:MoO_(x) BPAFLP2mBnfBPDBq-02:PCBBiF:[Ir(dppm)₂(acac)] 2mBnfBPDBq-02 BPhen LiF Alemitting 110 nm (=4:2) 20 nm 20 nm 10 nm 1 nm 200 nm element 3 20 nm(=0.7:0.3:0.05) (=0.8:0.2:0.05) 20 nm 20 nm

The light-emitting element of this example was sealed in a glove boxunder a nitrogen atmosphere so as not to be exposed to the air. Then,the operation characteristics of the light-emitting element weremeasured. Note that the measurement was carried out at room temperature(in an atmosphere kept at 25° C.).

FIG. 29 shows luminance-current density characteristics of thelight-emitting element 3. In FIG. 29, the horizontal axis indicatescurrent density (mA/cm²), and the vertical axis indicates luminance(cd/m²). FIG. 30 shows luminance-voltage characteristics. In FIG. 30,the horizontal axis indicates voltage (V) and the vertical axisindicates luminance (cd/m²). FIG. 31 shows current efficiency-luminancecharacteristics. In FIG. 31, the horizontal axis indicates luminance(cd/m²) and the vertical axis indicates current efficiency (cd/A). FIG.32 shows current-voltage characteristics. In FIG. 32, the horizontalaxis indicates voltage (V) and the vertical axis indicates current (mA).FIG. 33 shows external quantum efficiency-luminance characteristics. InFIG. 33, the horizontal axis indicates luminance (cd/m²) and thevertical axis indicates external quantum efficiency (%). Table 7 showsthe voltage (V), current density (mA/cm²), CIE chromaticity coordinates(x, y), current efficiency (cd/A), power efficiency (lm/W), and externalquantum efficiency (%) of the light-emitting element 3 at a luminance of1200 cd/m².

TABLE 7 External Current Current Power quantum Voltage density Luminanceefficiency efficiency efficiency (V) (mA/cm²) Chromaticity xChromaticity y (cd/m²) (cd/A) (lm/W) (%) Light- 2.9 1.4 0.55 0.44 120082 89 30 emitting element 3

The CIE chromaticity coordinates (x, y) at a luminance of 1200 cd/m² ofthe light-emitting element 3 were (0.55, 0.44) and the light-emittingelement 3 exhibited orange light emission. These results show thatorange light emission originating from [Ir(dppm)₂(acac)] was providedfrom the light-emitting element 3.

The measurement results of the operation characteristics show that thelight-emitting element 3 has high emission efficiency and a low drivevoltage.

A reliability test of the light-emitting element 3 was conducted. FIG.34 shows results of the reliability test. In FIG. 34, the vertical axisindicates normalized luminance (%) with an initial luminance of 100% andthe horizontal axis indicates driving time (h) of the element. In thereliability test, which was conducted at room temperature, thelight-emitting element 3 was driven under the conditions where theinitial luminance was set to 5000 cd/m² and the current density wasconstant. FIG. 34 shows that the light-emitting element 3 kept 87% ofthe initial luminance after 1100 hours. The results of the reliabilitytest show that the light-emitting element 3 has a long lifetime.

Reference Example

A method for synthesizingN-(1,1′-biphenyl-4-yl)-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-9,9-dimethyl-9H-fluoren-2-amine (abbreviation: PCBBiF) used in Examples 3 and 4 will bedescribed.

Step 1: Synthesis ofN-(1,1′-Biphenyl-4-yl)-9,9-dimethyl-N-phenyl-9H-fluoren-2-amine>

A synthesis scheme of Step 1 is shown in (x-1).

In a 1 L three-neck flask were placed 45 g (0.13 mol) ofN-(1,1′-biphenyl-4-yl)-9,9-dimethyl-9H-fluoren-2-amine, 36 g (0.38 mol)of sodium tert-butoxide, 21 g (0.13 mol) of bromobenzene, and 500 mL oftoluene. The mixture was degassed by being stirred while the pressurewas reduced, and after the degassing, the air in the flask was replacedwith nitrogen. Then, 0.8 g (1.4 mmol) ofbis(dibenzylideneacetone)palladium(0) and 12 mL (5.9 mmol) oftri(tert-butyl)phosphine (a 10 wt % hexane solution) were added.

The mixture was stirred at 90° C. under a nitrogen stream for 2 hours.Then, the mixture was cooled to room temperature, and a solid wasseparated by suction filteration. The obtained filtrate was concentratedto give approximately 200 mL of a brown liquid. The brown liquid wasmixed with toluene, and the resulting solution was purified usingCelite, alumina, and Florisil. The resulting filtrate was concentratedto give a pale yellow liquid. The pale yellow liquid was recrystallizedfrom hexane to give 52 g of target pale yellow powder in a yield of 95%.

Step 2: Synthesis ofN-(1,1′-Biphenyl-4-yl)-N-(4-bromophenyl)-9,9-dimethyl-9H-fluoren-2-amine

A synthesis scheme of Step 2 is shown in (x-2).

In a 1 L Erlenmeyer flask was placed 45 g (0.10 mol) ofN-(1,1′-biphenyl-4-yl)-9,9-dimethyl-N-phenyl-9H-fluoren-2-amine, whichwas dissolved in 225 mL of toluene by stirring while being heated. Afterthe solution was naturally cooled to room temperature, 225 mL of ethylacetate and 18 g (0.10 mol) of N-bromosuccinimide (abbreviation: NBS)were added, and the mixture was stirred at room temperature for 2.5hours. After the stirring, the mixture was washed three times with asaturated aqueous solution of sodium hydrogen carbonate and once withsaturated brine. Magnesium sulfate was added to the resulting organiclayer, and the mixture was left standing for 2 hours for drying. Themixture was subjected to gravity filteration to remove magnesiumsulfate, and the resulting filtrate was concentrated to give a yellowliquid. The yellow liquid was mixed with toluene, and this solution waspurified using Celite, alumina, and Florisil. The resulting solution wasconcentrated to give a pale yellow solid. The pale yellow solid wasrecrystallized from toluene/ethanol to give 47 g of target white powderin a yield of 89%.

Step 3: Synthesis of PCBBiF

A synthesis scheme of Step 3 is shown in (x-3).

In a 1 L three-neck flask were placed 41 g (80 mmol) ofN-(1,1′-biphenyl-4-yl)-N-(4-bromophenyl)-9,9-dimethyl-9H-fluoren-2-amineand 25 g (88 mmol) of 9-phenyl-9H-carbazole-3-boronic acid, to which 240mL of toluene, 80 mL of ethanol, and 120 mL of an aqueous solution ofpotassium carbonate (2.0 mol/L) were added. The mixture was degassed bybeing stirred while the pressure was reduced, and after the degassing,the air in the flask was replaced with nitrogen. Furthermore, 27 mg(0.12 mmol) of palladium(II) acetate and 154 mg (0.5 mmol) oftri(ortho-tolyl)phosphine were added. The mixture was degassed again bybeing stirred while the pressure was reduced, and after the degassing,the air in the flask was replaced with nitrogen. The mixture was stirredat 110° C. under a nitrogen stream for 1.5 hours.

After the mixture was naturally cooled to room temperature while beingstirred, the aqueous layer of the mixture was subjected to extractiontwice with toluene. The resulting solution of the extract and theorganic layer were combined and washed twice with water and twice withsaturated brine. Magnesium sulfate was added to the solution, and themixture was left standing for drying. The mixture was subjected togravity filteration to remove magnesium sulfate, and the resultingfiltrate was concentrated to give a brown solution. The brown solutionwas mixed with toluene, and the resulting solution was purified usingCelite, alumina, and Florisil. The resulting filtrate was concentratedto give a pale yellow solid. The pale yellow solid was recrystallizedfrom ethyl acetate/ethanol to give 46 g of target pale yellow powder ina yield of 88%.

By a train sublimation method, 38 g of the obtained pale yellow powderwas purified. In the sublimation purification, the pale yellow powderwas heated at 345° C. under a pressure of 3.7 Pa with an argon flow rateof 15 mL/min. After the sublimation purification, 31 g of a target paleyellow solid was obtained at a collection rate of 83%.

This compound was identified asN-(1,1′-biphenyl-4-yl)-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-9,9-dimethyl-9H-fluoren-2-amine (abbreviation: PCBBiF), which was the target of thesynthesis, by nuclear magnetic resonance (NMR) spectroscopy.

¹H NMR data of the obtained pale yellow solid are as follows:

¹H NMR (CDCl₃, 500 MHz): δ=1.45 (s, 6H), 7.18 (d, J=8.0 Hz, 1H),7.27-7.32 (m, 8H), 7.40-7.50 (m, 7H), 7.52-7.53 (m, 2H), 7.59-7.68 (m,12H), 8.19 (d, J=8.0 Hz, 1H), 8.36 (d, J=1.1 Hz, 1H).

REFERENCE NUMERALS

201: first electrode, 203: EL layer, 203 a: first EL layer, 203 b:second EL layer, 205: second electrode, 207: intermediate layer, 301:hole-injection layer, 302: hole-transport layer, 303: light-emittinglayer, 304: electron-transport layer, 305: electron-injection layer,401: support substrate, 403: light-emitting element, 405: sealingsubstrate, 407: sealing material, 409 a: first terminal, 409 b: secondterminal, 411 a: light extraction structure, 411 b: light extractionstructure, 413: planarization layer, 415: space, 417: auxiliary wiring,419: insulating layer, 421: first electrode, 423: EL layer, 425: secondelectrode, 501: support substrate, 503: light-emitting element, 504:light-emitting element, 505: sealing substrate, 506: desiccant, 507:sealing material, 509: FPC, 511: insulating layer, 513: insulatinglayer, 515: space, 517: wiring, 519: partition, 521: first electrode,523: EL layer, 525: second electrode, 531: black matrix, 533: colorfilter, 535: overcoat layer, 541 a: transistor, 541 b: transistor, 542:transistor, 543: transistor, 551: light-emitting portion, 551 a:light-emitting portion, 551 b: light-emitting portion, 552: drivercircuit portion, 553: driver circuit portion, 561: first electrode, 563:EL layer, 565: second electrode, 1100: glass substrate, 1101: firstelectrode, 1103: second electrode, 1111: hole-injection layer, 1112:hole-transport layer, 1113: light-emitting layer, 1114:electron-transport layer, 1115: electron-injection layer, 7100:television device, 7101: housing, 7102: display portion, 7103: stand,7111: remote controller, 7200: computer, 7201: main body, 7202: housing,7203: display portion, 7204: keyboard, 7205: external connection port,7206: pointing device, 7300: portable game machine, 7301 a: housing,7301 b: housing, 7302: joint portion, 7303 a: display portion, 7303 b:display portion, 7304: speaker portion, 7305: recording medium insertionportion, 7306: operation key, 7307: connection terminal, 7308: sensor,7400: cellular phone, 7401: housing, 7402: display portion, 7403:operation button, 7404: external connection port, 7405: speaker, 7406:microphone, 7500: tablet terminal, 7501 a: housing, 7501 b: housing,7502 a: display portion, 7502 b: display portion, 7503: hinge, 7504:power switch, 7505: operation key, 7506: speaker, 7601: lighting device,7602: lighting device, 7603: desk lamp, 7604: planar lighting device,7701: lighting portion, 7703: support, 7705: support base.

This application is based on Japanese Patent Application serial no.2013-178449 filed with Japan Patent Office on Aug. 29, 2013, andJapanese Patent Application serial no. 2014-095259 filed with JapanPatent Office on May 2, 2014, the entire contents of which are herebyincorporated by reference.

1. A compound represented by formula (G4):

wherein: one of R⁷ to R¹⁰ represents a substituent represented byformula (G4-1); R¹ to R⁶ and the others of R⁷ to R¹⁰ separatelyrepresent any one of hydrogen, an alkyl group having 1 to 6 carbonatoms, a cycloalkyl group having 3 to 6 carbon atoms, and an aryl grouphaving 6 to 13 carbon atoms; R²⁰ and R²¹ separately represent an alkoxygroup having 1 to 6 carbon atoms and are bonded to each other to form aring.
 2. The compound according to claim 1, wherein the aryl grouphaving 6 to 13 carbon atoms is unsubstituted or substituted by any oneof an alkyl group having 1 to 6 carbon atoms, a cycloalkyl group having3 to 6 carbon atoms, and an aryl group having 6 to 13 carbon atoms. 3.The compound according to claim 1, wherein the alkoxy group having 1 to6 carbon atoms is unsubstituted or substituted by any one of an alkylgroup having 1 to 6 carbon atoms, a cycloalkyl group having 3 to 6carbon atoms, and an aryl group having 6 to 13 carbon atoms.
 4. Thecompound according to claim 1, wherein: R¹⁰ represents a substituentrepresented by formula (G4-1); R¹ to R⁹ separately represent any one ofhydrogen, an alkyl group having 1 to 6 carbon atoms, a cycloalkyl grouphaving 3 to 6 carbon atoms, and an aryl group having 6 to 13 carbonatoms.
 5. The compound according to claim 1, wherein the compound isrepresented by formula (201),


6. A compound represented by formula (G4):

wherein: one of R⁷ to R¹⁰ represents a substituent represented byformula (G4-1); R¹ to R⁶ and the others of R⁷ to R¹⁰ separatelyrepresent any one of hydrogen, an alkyl group having 1 to 6 carbonatoms, a cycloalkyl group having 3 to 6 carbon atoms, and an aryl grouphaving 6 to 13 carbon atoms; R²⁰ and R²¹ separately represent an alkoxygroup having 1 to 6 carbon atoms.
 7. The compound according to claim 6,wherein the aryl group having 6 to 13 carbon atoms is unsubstituted orsubstituted by any one of an alkyl group having 1 to 6 carbon atoms, acycloalkyl group having 3 to 6 carbon atoms, and an aryl group having 6to 13 carbon atoms.
 8. The compound according to claim 6, wherein thealkoxy group having 1 to 6 carbon atoms is unsubstituted or substitutedby any one of an alkyl group having 1 to 6 carbon atoms, a cycloalkylgroup having 3 to 6 carbon atoms, and an aryl group having 6 to 13carbon atoms.
 9. The compound according to claim 6, wherein: R¹⁰represents a substituent represented by formula (G4-1); R¹ to R⁹separately represent any one of hydrogen, an alkyl group having 1 to 6carbon atoms, a cycloalkyl group having 3 to 6 carbon atoms, and an arylgroup having 6 to 13 carbon atoms.